Update git submodules

* Update charm-keystone from branch 'master'
  to 074bb1f26c7fb4991eaa057bdd3e1d9b96b0766d
  - Merge "Use unittest.mock instead of mock"
  - Use unittest.mock instead of mock
    
    The mock third party library was needed for mock support in py2
    runtimes. Since we now only support py36 and later, we can use the
    standard lib unittest.mock module instead.
    
    Note that https://github.com/openstack/charms.openstack is used during tests
    and he need `mock`, unfortunatelly it doesn't declare `mock` in its
    requirements so it retrieve mock from other charm project (cross dependency).
    So we depend on charms.openstack first and when
    Ib1ed5b598a52375e29e247db9ab4786df5b6d142 will be merged then CI
    will pass without errors.
    
    Drop Python 3.5 testing.
    
    Rework some unit tests that use unittest.mock features not introduced
    until Python 3.7.
    
    Depends-On: Ib1ed5b598a52375e29e247db9ab4786df5b6d142
    Change-Id: I029c77ed697620725dc040d1849a691eb10c9351

charm-keystone

@@ -1 +1 @@
-Subproject commit 24a263a14dbdadc2e277cdb6759b5b23b9b00011
+Subproject commit 074bb1f26c7fb4991eaa057bdd3e1d9b96b0766d