Move logic for ceph-client-relation-changed into hooks.py
 * Make it testable
 * Test it
 * Bump revision
Clean up tests and hooks, move ceph-client-relation-broken into hooks.py too.
Use addCleanup to undo the monkey matching
s/use/used/ (tealeg's review)
Merged fix-ceph-relation-error [r=bjornt,tealeg][a=adam-collard]

Move ceph-relation-changed and ceph-relation-broken hooks into hooks.py and therefore more easily testable.
Fix call to config_changed() in registration relation
Merged fix-registration-relation [r=jseutter] [f=1256109]

Fixed call to config_changed() in the registration relation.
Add an object for running the hooks, so that tests and juju runs the hooks in the same way.
Clear computer title and remove juju info when departing the relation.
Document the hook.
Document the tests.
Typos.
Lint.
Merged relation-depart-no-register [r=adam-collard,tribaal] [f=1255972].

Clear relation data when departing the relation.

Delete all data related to the container relation when departing it. The
computer title and the juju info file contains information about the remote
unit that landscape-client is related to. If the relation is removed, that
information is not valid anymore and should be removed.

This prevents the client from trying to register again when the config-changed
hook is run, which can happen when services are destroyed.

I also changed the way hooks are run, so that tests and the real Juju process
runs hooks the same way.