update interface.yaml with ignores and maintainer

The ignores removes all files that are not relevant to
the interface from the built charm, and thus, the
runtime imports of the interface bits

Change-Id: I4d5c58fff7d05dc10eea54567fbabb579a9ddd71

interface.yaml

@@ -1,3 +1,13 @@
 name: ceph-client
 summary: Ceph Client Interface
-version: 1
+version: 1
+maintainer: OpenStack Charmers <openstack-discuss@lists.openstack.org>
+ignore:
+  - 'unit_tests'
+  - 'Makefile'
+  - '.testr.conf'
+  - 'test-requirements.txt'
+  - 'tox.ini'
+  - '.gitignore'
+  - '.gitreview'
+  - '.unit-state.db'