Remove experimental flag from share groups feature

The share groups functionality will no longer be considered
experimental. The existent functional tests were modified to accomplish
with this feature graduation.

Change-Id: Ideba68c0481345e808f185195eea68e879155cf1
Partially-Implements: bp graduate-share-groups-feature
diff --git a/manila_tempest_tests/config.py b/manila_tempest_tests/config.py
index 042be5a..6973092 100644
--- a/manila_tempest_tests/config.py
+++ b/manila_tempest_tests/config.py
@@ -30,7 +30,7 @@
                help="The minimum api microversion is configured to be the "
                     "value of the minimum microversion supported by Manila."),
     cfg.StrOpt("max_api_microversion",
-               default="2.53",
+               default="2.55",
                help="The maximum api microversion is configured to be the "
                     "value of the latest microversion supported by Manila."),
     cfg.StrOpt("region",