taskd/clone.sh: record info for clones exceeding limits

taskd/clone.sh: record info for clones exceeding limits

When a clone exceeds an allowed size limit, all objects are
immediately purged to avoid using disk space.

Remember that it was a clone that failed due to an exceeded
limit by using ".clone_failed_exceeds_limit" instead of
".clone_failed" and emit copies of the exceeds reason(s) to
both ".clone_failed_exceeds_limit" and ".clonelog" to make it
easy to recover the information without needing the failure
message that's emailed.

At the same time, remove the ".clone_failed" file to prevent
having a "Restart Mirroring" button show up on the project edit
page.  Restarting the mirror will not cure the fact that the
source respository exceeds allowed limits.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>