distgit: Block push of branches named 'origin/*'

We already use the update hook for gitolite.

This introduces a new update hook, which merely chains the gitolite one,
and a new one to block pushes to badly named branches.

The new hook was written originally by Till Maas.

https://fedorahosted.org/rel-eng/ticket/4071
Rearrange some tasks

We have a gitolite/check_fedmsg_hooks role, which installs a script and
schedules it.

Turns out, this script does more than just checking the fedmsg hooks,
depending on the command-line arguments used when running it.

As such, it makes sense to separate it out into its own role, and make
the gitolite/check_fedmsg_hooks role (and any other one using the
script) depend on it.

For example, this script is used for Fedora Hosted (still in Puppet),
and will soon be used for a new distgit hook check.
git/checks: Check for the update hooks

We are now setting up distgit (and possibily other things like
Fedora Hosted) to use a more elaborate system of update hooks.

This updates the checking script so it is capable of ensuring this set
up.
distgit: Schedule a weekly check of the update hooks

This allows ensuring over time that all repositories have the right
update hooks set up.