Setup snapshot extra specs only if required

For legacy reasons we always included snapshot_support
and create_share_from_snapshot_support in all the
share types the tests created. These extra-specs are
no different from any other optional extra-specs in
manila, atleast since API version 2.24 (snapshot_support
was "implied"/"required" until API version 2.23). 2.24
is a really old version to support for tempest testing.

Since we always use the latest API version to create the
share types necessary, we only ever need 1 required
extra spec (driver_handles_share_servers) - lets supply
the rest only within tests that need to test snapshots
and shares from snapshots.

This patch also adds missing skip decorators for share
group tests that were testing snapshots.

Change-Id: Ifaceab574e3242e44a9cf1bea77a4be9e505d8b8
Related-Bug: #1922784
Signed-off-by: Goutham Pacha Ravi <gouthampravi@gmail.com>
diff --git a/manila_tempest_tests/config.py b/manila_tempest_tests/config.py
index 7aaf5c9..5a9087c 100644
--- a/manila_tempest_tests/config.py
+++ b/manila_tempest_tests/config.py
@@ -27,7 +27,9 @@
     cfg.StrOpt("min_api_microversion",
                default="2.0",
                help="The minimum api microversion is configured to be the "
-                    "value of the minimum microversion supported by Manila."),
+                    "value of the minimum microversion supported by Manila. "
+                    "This value is only used to validate the versions "
+                    "response from Manila."),
     cfg.StrOpt("max_api_microversion",
                default="2.61",
                help="The maximum api microversion is configured to be the "