git-codereview: print git version when test fails to execute command
git-codereview: print git version when test fails to execute command

Sample output when modifying one of the git commands:

--- FAIL: TestSync (0.36s)
	util_test.go:250: git-codereview change work
	util_test.go:250: git-codereview sync
	util_test.go:207: in git-client/, ran [git add --does-not-exist file1] with git version 1.9.1:
		exit status 129
		error: unknown option `does-not-exist'
		usage: git add [options] [--] <pathspec>...

		    -n, --dry-run         dry run
		    -v, --verbose         be verbose

		    -i, --interactive     interactive picking
		    -p, --patch           select hunks interactively
		    -e, --edit            edit current diff and apply
		    -f, --force           allow adding otherwise ignored files
		    -u, --update          update tracked files
		    -N, --intent-to-add   record only the fact that the path will be added later
		    -A, --all             add changes from all tracked and untracked files
		    --ignore-removal      ignore paths removed in the working tree (same as --no-all)
		    --refresh             don't add, only refresh the index
		    --ignore-errors       just skip files which cannot be added because of errors
		    --ignore-missing      check if - even missing - files are ignored in dry run

Updates golang/go#9602.

Change-Id: Ibeb93b1f3f4da43d1f95fd0eb5f2c372210cd6b3
Reviewed-on: https://go-review.googlesource.com/9952
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
Run-TryBot: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/review