Revert "Removed fixed size arg from mkimage-gcp script."

[rn]

Reverts #3300

This does not work and the CI fails building the GCP image (see #3451). Enabling more logging in mkimage-gcp gives the following error:

supermin: build: visiting /usr/lib/x86_64-linux-gnu/guestfs/supermin.d/packages type uncompressed packages
supermin: build: visiting /usr/lib/x86_64-linux-gnu/guestfs/supermin.d/packages-hfsplus type uncompressed packages
supermin: build: visiting /usr/lib/x86_64-linux-gnu/guestfs/supermin.d/packages-reiserfs type uncompressed packages
supermin: build: visiting /usr/lib/x86_64-linux-gnu/guestfs/supermin.d/packages-xfs type uncompressed packages
supermin: build: visiting /usr/lib/x86_64-linux-gnu/guestfs/supermin.d/udev-rules.tar.gz type gzip base image (tar)
supermin: mapping package names to installed packages
supermin: resolving full list of package dependencies
supermin: build: 192 packages, including dependencies
supermin: build: 10676 files
supermin: build: 6472 files, after matching excludefiles
supermin: build: 6475 files, after adding hostfiles
supermin: build: 6475 files, after removing unreadable files
supermin: build: 6478 files, after munging
supermin: kernel: picked kernel vmlinuz-4.9.0-5-amd64
supermin: kernel: picked modules path /lib/modules/4.9.0-5-amd64
supermin: kernel: kernel_version 4.9.0-5-amd64
supermin: kernel: modules /lib/modules/4.9.0-5-amd64
supermin: ext2: creating empty ext2 filesystem '/var/tmp/.guestfs-0/appliance.d.fchyrekj/root'
supermin: ext2: populating from base image
supermin: error: statvfs: No space left on device: /var/tmp/.guestfs-0/appliance.d.fchyrekj/root
libguestfs: error: /usr/bin/supermin exited with error status 1, see debug messages above
libguestfs: trace: launch = -1 (error)

I've tried a number of different options for sizing and none seem to work.

I suggest to revert this PR for now.

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "revert-3300-bugfix-make-gcp-size-limit" git@github.com:linuxkit/linuxkit.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[rn]

CI fails with a lot of messages like:

[+ 58m 25s] [STDERR  ] 2019-12-20T18:58:21.115849387Z: + linuxkit run -mem 2048 -disk size=2G containerd
[+ 58m 27s] [STDERR  ] 2019-12-20T18:58:23.216462041Z: qemu-system-x86_64: cannot set up guest memory 'pc.ram': Out of memory
[+ 58m 27s] [STDERR  ] 2019-12-20T18:58:23.218141129Z: time="2019-12-20T18:58:23Z" level=fatal msg="exit status 1"

basically unable to allocate memory for qemu

[rn]

Hmm, this time the CI timed out. Hit rebuild again

[justincormack]

It timed out again...

[rn]

rebuilding again, now that I'm back in front of a computer

[rn]

Odd, the CI timed out again and there seems to be a huge jump in time when starting to run the containerd test:

[+ 48m 14s] [STDERR  ] 2019-12-31T11:23:58.842663030Z: + linuxkit build -format kernel+initrd -name containerd test.yml
[+ 48m 14s] [STDERR  ] 2019-12-31T11:23:58.893667175Z: Extract kernel image: docker.io/linuxkit/kernel:4.19.90
[+ 48m 15s] [STDERR  ] 2019-12-31T11:24:00.263410975Z: time="2019-12-31T11:24:00Z" level=warning msg="targets/justin metadata is nearing expiry, you should re-sign the role metadata"
[+ 48m 19s] [STDERR  ] 2019-12-31T11:24:04.323002207Z: Add init containers:
[+ 48m 19s] [STDERR  ] 2019-12-31T11:24:04.323115352Z: Process init image: docker.io/linuxkit/init:1d8e0532ca588c5ad0d9ca6038349a70bb7ac626
[+ 48m 21s] [STDERR  ] 2019-12-31T11:24:06.062857957Z: Process init image: docker.io/linuxkit/runc:c1f0db27e71d948f3134b31ce76276f843849b0a
[+ 48m 22s] [STDERR  ] 2019-12-31T11:24:07.101878231Z: time="2019-12-31T11:24:07Z" level=warning msg="targets/riyaz metadata is nearing expiry, you should re-sign the role metadata"
[+ 48m 23s] [STDERR  ] 2019-12-31T11:24:07.679191588Z: Process init image: docker.io/linuxkit/containerd:751de142273e1b5d2d247d2832d654ab92e907bc
[+ 48m 24s] [STDERR  ] 2019-12-31T11:24:08.723083305Z: time="2019-12-31T11:24:08Z" level=warning msg="targets/riyaz metadata is nearing expiry, you should re-sign the role metadata"
[+ 48m 25s] [STDERR  ] 2019-12-31T11:24:10.039251718Z: Process init image: docker.io/linuxkit/ca-certificates:v0.7
[+ 48m 26s] [STDERR  ] 2019-12-31T11:24:11.068373520Z: time="2019-12-31T11:24:11Z" level=warning msg="targets/riyaz metadata is nearing expiry, you should re-sign the role metadata"
[+ 48m 27s] [STDERR  ] 2019-12-31T11:24:11.551918754Z: Add onboot containers:
[+ 48m 27s] [STDERR  ] 2019-12-31T11:24:11.552066196Z:   Create OCI config for linuxkit/dhcpcd:v0.7
[+ 48m 28s] [STDERR  ] 2019-12-31T11:24:13.087606420Z:   Create OCI config for linuxkit/sysctl:v0.7
[+ 48m 30s] [STDERR  ] 2019-12-31T11:24:14.566211948Z:   Create OCI config for linuxkit/format:65b9e0a76d0b9fb8ac5c5f3bc8d3131109290f56
[+ 48m 31s] [STDERR  ] 2019-12-31T11:24:16.354179196Z:   Create OCI config for linuxkit/mount:v0.7
[+ 48m 33s] [STDERR  ] 2019-12-31T11:24:18.024984817Z:   Create OCI config for linuxkit/test-containerd:ac28577db835db4a87b6ba390ad15f3369c1585a
[+ 48m 34s] [STDERR  ] 2019-12-31T11:24:19.157154947Z: time="2019-12-31T11:24:19Z" level=warning msg="targets/riyaz metadata is nearing expiry, you should re-sign the role metadata"
[+ 48m 45s] [STDERR  ] 2019-12-31T11:24:30.079653619Z:   Create OCI config for linuxkit/poweroff:b498d30dd9660090565537fceb9e757618737a85
[+ 48m 46s] [STDERR  ] 2019-12-31T11:24:31.120220732Z: time="2019-12-31T11:24:31Z" level=warning msg="targets/riyaz metadata is nearing expiry, you should re-sign the role metadata"
[+ 48m 47s] [STDERR  ] 2019-12-31T11:24:31.607453843Z: Create outputs:
[+ 49m 28s] [STDERR  ] 2019-12-31T11:25:13.022445386Z:   containerd-kernel containerd-initrd.img containerd-cmdline
[+ 49m 28s] [STDERR  ] 2019-12-31T11:25:13.399853673Z: + linuxkit run -mem 2048 -disk size=2G containerd
[+ 83m 36s] [STDERR  ] 2019-12-31T11:59:20.693674497Z: main-loop: WARNING: I/O thread spun for 1000 iterations
[+ 83m 37s] [STDERR  ] 2019-12-31T11:59:21.964030523Z: + RESULT=[    0.000000] Linux version 4.19.90-linuxkit (root@buildkitsandbox) (gcc version 8.3.0 (Alpine 8.3.0)) #1 SMP Wed Dec 18 20:15:48 UTC 2019
[+ 83m 37s] [STDERR  ] 2019-12-31T11:59:21.964207488Z: [    0.000000] Command line: console=ttyS0 console=ttyAMA0