command: filter projects by active manifest groups

`repo forall <proj>` will look up all <proj> in the manifest for all
manifest groups regardless of which are active.  If <proj> is checked
out to different locations depending on the group, this ultimately
fails as we're unable to locate all of them.

Simple fix is to only include projects that match the manifest groups
that we already passed down & initialized to the active set, and that
we already use when getting the default project list.

Bug: https://crbug.com/gerrit/11677
Bug: https://crbug.com/1011226
Change-Id: I975f10f9a9e5a1cad7d87344123f8003732dab27
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/239652
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: David Pursehouse <dpursehouse@collab.net>