Remove empty lines from git log output

assert_one_change would falsely believe there was a commit when git log returned empty input
because python's strip method returns an array containing an empty string if nothing matches the separator
for example = "".split("\n") returns [''].

I remove empty strings to allow the check to respond to no non-pushed commits

Change-Id: I0d5608acb1728e77f20d9de71c6c23ec4da1c798
Merge "Remove empty lines from git log output"