rebase: add basic coloring output
rebase: add basic coloring output

This uses coloring style like we use in grep/forall already.

Change-Id: I317e2e47567a30c513083c48e7c7c40b091bb29a
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/238555
Reviewed-by: David Pursehouse <e7b5c6a4a3dbaca972851f8c075e19915752593f@collab.net>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>

mer-tools/git-repo,TheQtCompany/git-repo,GerritCodeReview/git-repo,lewixliu/git-repo,mer-tools/git-repo,codetutil/git-repo,aosp-mirror/tools_repo,gabbayo/git-repo,TheQtCompany/git-repo,lewixliu/git-repo,couchbasedeps/git-repo,aosp-mirror/tools_repo,GerritCodeReview/git-repo,codetutil/git-repo,gabbayo/git-repo,couchbasedeps/git-repo,lipro-yocto/git-repo,lipro-yocto/git-repo