[Share groups] Add scheduler filter ConsistentSnapshotFilter

That will be used for scheduling share groups based on their possibility
to create consistent snapshots.

Also apply following tempest plugin changes:
- Add new 'capability_sg_consistent_snapshot_support' tempest config
option, that will be used for creation of new share group types and used
to prove that scheduling works as expected.
- Fix some share group test attributes from 'only API involved' to
  'API and Backend are involved', because it is so indeed.

Change-Id: I05553c308ae40c4ddc2c6469ff1c1a3da36a87da
Partially-Implements BP manila-share-groups
diff --git a/manila_tempest_tests/tests/api/base.py b/manila_tempest_tests/tests/api/base.py
index de298da..236351d 100644
--- a/manila_tempest_tests/tests/api/base.py
+++ b/manila_tempest_tests/tests/api/base.py
@@ -595,6 +595,11 @@
                                 group_specs=None, client=None,
                                 cleanup_in_class=True, **kwargs):
         client = client or cls.shares_v2_client
+        if group_specs is None:
+            group_specs = {
+                'consistent_snapshot_support': (
+                    CONF.share.capability_sg_consistent_snapshot_support),
+            }
         share_group_type = client.create_share_group_type(
             name=name,
             share_types=share_types,