tests/lib: introduce helpers for setting up /dev/random using /dev/urandom in project prepare

[bboozzoo]

The hosts used for testing may run out of entropy in /dev/random, thus causing
any crypto operations to potentially block. Since we do not need a high quality
RNG source for the tests, set up /dev/random to be the same as /dev/urandom in
project prepare and restore it back to the proper state in project restore
phase.

[zyga]

+1 with note, please check before merging

[zyga]

This is probably not correct since some distributions don't use proper random devices. We should probably mv /dev/random /dev/random.bak or .orig and then mv them back.

In any case, this is my suggestion, LGTM

[codecov-io]

Codecov Report

Merging #4354 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4354   +/-   ##
=======================================
  Coverage   78.05%   78.05%           
=======================================
  Files         450      450           
  Lines       30899    30899           
=======================================
  Hits        24118    24118           
  Misses       4772     4772           
  Partials     2009     2009

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[zyga]

LGTM

[zyga]

Ha, much much nicer :)

[zyga]

The device numbers are valid for urandom

[bboozzoo]

Well, at least it didn't timeout this time. The tasks that were getting stuck before, all passed now. What has failed is:

2017-12-11 13:35:04 Successful tasks: 1581
2017-12-11 13:35:04 Aborted tasks: 1
2017-12-11 13:35:04 Failed tasks: 1
    - linode:ubuntu-core-16-64:tests/main/interfaces-snapd-control-with-manage
2017-12-11 13:35:04 Failed task prepare: 1
    - linode:fedora-26-64:tests/main/revert-sideload
error: unsuccessful run

Looks unrelated, so I've restarted the build.

[bboozzoo]

FWIW, the travis job was filing before as the create-key/snap-sign/completion prepare were taking too long. Collected debug output suggests that the /dev/random node was not changed at all. This is either the fixup_dev_random applied in prepare was reverted (although I did not manage to track down the code where this could happen), didn't run, or project restore was run (?).

Debug log in question:

2017-12-11 11:27:34 Error executing linode:debian-9-64:tests/main/snap-sign : 
-----
+ echo 'Creating a new key without a password'
Creating a new key without a password
+ expect -f create-key.exp
spawn snap create-key

Passphrase: 

Confirm passphrase: 
<kill-timeout reached>
-----
travis_time:end:a4df1e52:start=1512990455705312850,finish=1512991654836096494,duration=1199130783644
travis_fold:end:fold-a4df1e52
.
travis_time:end:aaff80bf:start=1512991654103974079,finish=1512991655057084868,duration=953110789
travis_time:start:e3cf5337
2017-12-11 11:27:35 Restoring linode:ubuntu-16.04-32:tests/main/known-remote...
travis_fold:start:fold-d6a4eb69
travis_time:start:d6a4eb69
2017-12-11 11:27:35 Debug output for linode:debian-9-64:tests/main/snap-sign : 
-----
+ . /home/gopath/src/github.com/snapcore/snapd/tests/lib/random.sh
+ debug_random
+ sysctl kernel.random.entropy_avail
kernel.random.entropy_avail = 44
+ ls -l /dev/random /dev/urandom
crw-rw-rw- 1 root root 1, 8 Dec 11 11:06 /dev/random
crw-rw-rw- 1 root root 1, 9 Dec 11 11:06 /dev/urandom
++ pidof gpg-agent
+ pids=9700
+ for p in $pids
+ ps -q 9700
  PID TTY          TIME CMD
 9700 ?        00:00:00 gpg-agent
+ ls -l /proc/9700/fd
total 0
lr-x------ 1 root root 64 Dec 11 11:27 0 -> /dev/null
l-wx------ 1 root root 64 Dec 11 11:27 1 -> /dev/null
l-wx------ 1 root root 64 Dec 11 11:27 2 -> /dev/null
lrwx------ 1 root root 64 Dec 11 11:27 3 -> socket:[42935]
lrwx------ 1 root root 64 Dec 11 11:27 4 -> socket:[42937]
lrwx------ 1 root root 64 Dec 11 11:27 5 -> socket:[42939]
lrwx------ 1 root root 64 Dec 11 11:27 6 -> socket:[42941]
lr-x------ 1 root root 64 Dec 11 11:27 7 -> anon_inode:inotify
lrwx------ 1 root root 64 Dec 11 11:27 8 -> socket:[42946]
lr-x------ 1 root root 64 Dec 11 11:27 9 -> /dev/random
+ '[' 1 = 1 ']'
+ echo '# journal messages for snapd'