rebase: add --fail-fast support
rebase: add --fail-fast support

Lets switch the default rebase behavior to align with our new sync
behavior: we try to rebase all projects by default and exit/summarize
things at the very end if there were any errors.  Or if people want
to exit immediately, they can use the new --fail-fast option.

Change-Id: I436ac563f972b45de6ce9ad74da1e4870e584902
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/238553
Reviewed-by: David Pursehouse <e7b5c6a4a3dbaca972851f8c075e19915752593f@collab.net>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>

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