gits: use git plumbing commands

Instead of 'git status' and 'git branch', which change their output
depending on the git version and locale, use the low-level plumbing
commands.

'gits status' output is exactly the same, 'gits rebase' output is
a bit less redundant now (that was easier to implement).

Change-Id: I42544313d14db126c99e2d9a02b8f63031944947
1 file changed