Update to bazel-0.18.0 and use try-import

[perfinion]

Bazel-0.18.0 adds a try-import option that will non-fatally try and
import a file. Use this for the configure options so that .bazelrc does
not need to change. ./configure rewriting .bazelrc makes using the git
repo annoying because the file is changed.

Also optionally import a /.bazelrc.user file that is gitignored so
user-specific options can go in there.

Fixes: #22762
Fixes: #22906
Signed-off-by: Jason Zaman jason@perfinion.com

[perfinion]

Bazel-0.18.0 is due out on monday. Lets merge this in as soon as we can. Having ./configure edit the .bazelrc is causing a lot of annoyance.

[gunan]

Bumping the minimum required version to the cutting edge version has caused many issues before.
Due to this, I am against this change in minimum requirement until at least bazel 0.19 is out.

[perfinion]

@gunan okay fair enough. In that case bazel-0.18.0 has temporarily added back reading tools/bazel.rc so I'll make a separate PR to move things back there then when 0.19.0 is out we do this change.

[yongtang]

The issue #22449 might be related (needs bazel update > 0.17.1).

[yongtang]

@gunan @perfinion It looks like bazel 0.19.0 has been released:
bazelbuild/bazel#6116

[meteorcloudy]

Since Bazel 0.19.0 has come out, can we try again to merge this change?
Currently, TensorFlow has been disabled from Bazel downstream projects due to the bazelrc file change, I wound like to bring it back before we cut 0.20.0.

[meteorcloudy]

@perfinion Is this PR going to fix TF build with Bazel 0.19.0? If so, can you try to resolve the conflicts? Thanks!

[perfinion]

@gunan okay to merge now? bazel 0.19 is out

[meteorcloudy]

We need to upgrade Bazel to 0.18.1 on all CI machines before merging this.

[angerson]

@meteorcloudy Is that upgrade only required on TensorFlow's CI machines?
@av8ramit What do we need to do to upgrade Bazel on the CI machines?

[meteorcloudy]

@angersson Yes, in order not to break anything, we should upgrade Bazel on all TF CI machines.
But, of course, after merging this change, anyone wants to build TensorFlow from HEAD needs at least 0.18.X.

[gunan]

@meteorcloudy, then this change needs to be done internally, to be able to make all the test infra changes atomicly.
Would you like to import this change and make those upgrades? @yifeif can provide the instructions to start by importing this change internally.

[meteorcloudy]

Sounds good, I can help import this change and make those upgrades!

[tensorflowbutler]

Nagging Assignee @case540: It has been 15 days with no activity and this issue has an assignee. Please update the label and/or status accordingly.

[perfinion]

I updated this. min version is 0.18.0, max is 0.20.0. I added an env variable to skip the max bazel version check to make testing new versions easier.
User-specific changes should go in .bazelrc.user which is gitignored. Nothing should edit .bazelrc anymore since it is no longer gitignored.

Looks like the the CI builds are all failing, do they need to be upgraded?

[meteorcloudy]

Yes, looks like Bazel is still 0.16.1 on Ubuntu. Can we upgrade to the latest Bazel on all CI machines?
@gunan @yifeif

[yifeif]

@meteorcloudy I'll send you a change to upgrade ubuntu to the same bazel version internally. Ping me if you need help with pulling this PR in.

[gunan]

While minimum is 0.18, I still want our dockerfiles to have 0.20 because 0.18 and 19 have some bugs

[meteorcloudy]

@perfinion The Bazel version on CI machines has been upgraded now, can you rebase this PR again then we can rerun the presubmit for it. ;)