Update git submodules

* Update charm-ceilometer from branch 'master'
  to c4f153e5820f4103f0e7e1a16b2b959477f0ed3a
  - Ensure get_requests_for_local_unit doesn't fail on incomplete relation
    
    This is a rebuild/make sync for charms to pickup the fix in charmhelpers to fix
    any inadvertant accesses of ['ca'] in the relation data before it is available
    from vault in the certificates relation.  Fix in charmhelpers is in [1].
    
    [1] juju/charm-helpers#824
    Closes-Bug: #2028683
    
    Change-Id: I3393fc63fa066b15f3e67c526ab3f2abe0ead028