git: Don't show clean error if failing to translate commit hash

[jerry-skydio]

In order to show a better error to the user, catch shell
return codes and raise RevupUsageException.

Topic: catch
Reviewers: brian-k, aaron

[jerry-skydio]

Reviews in this chain:
└#115 git: Don't show clean error if failing to translate commit hash

[jerry-skydio]

#	head	base	diff	date	summary
0	426801fa	92bd9efb	diff	Apr 14 14:19 PM	1 file changed, 6 insertions(+), 2 deletions(-)