launcher: make missing .repo/repo/repo an error
launcher: make missing .repo/repo/repo an error

If the specified repo dir doesn't actually have a `repo` program,
we only show a warning before continuing on, and then we fail in
weird ways.  Since we really need the repo dir to contain repo,
have this be fatal and delete the results.

Bug: https://crbug.com/gerrit/13526
Change-Id: Icee4cba96136d470cbb459a81918c40205078f98
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/343538
Reviewed-by: LaMont Jones <01939f9990a33aa2509cfaed21d2f9ba201a2b37@google.com>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>

lewixliu/git-repo,GerritCodeReview/git-repo,GerritCodeReview/git-repo,lewixliu/git-repo