git-build: mark as finished when log is flushed

Previously, tests would occasionally fail on TravisCI perhaps because
the log hasn't been flushed before the test attempts to read it.

Now we don't mark the test as done until the log is flushed.
Merge git-build--finish-when-log-is-flushed (#55) into master

git-build: mark as finished when log is flushed

Previously, tests would occasionally fail on TravisCI perhaps because
the log hasn't been flushed before the test attempts to read it.

Now we don't mark the test as done until the log is flushed.