[Tempest] Make share size configurable in scenario tests

The scenario tests missing a way to configure
the share size created during the test.

Change-Id: I58d433a39037cbdb4ad92f956cfc27c54739fe1a
Closes-bug: #1642548
diff --git a/manila_tempest_tests/tests/scenario/manager_share.py b/manila_tempest_tests/tests/scenario/manager_share.py
index 14fb34d..50a3a8a 100644
--- a/manila_tempest_tests/tests/scenario/manager_share.py
+++ b/manila_tempest_tests/tests/scenario/manager_share.py
@@ -50,7 +50,7 @@
         cls.shares_admin_v2_client = shares_v2_client.SharesV2Client(
             cls.os_admin.auth_provider)
 
-    def _create_share(self, share_protocol=None, size=1, name=None,
+    def _create_share(self, share_protocol=None, size=None, name=None,
                       snapshot_id=None, description=None, metadata=None,
                       share_network_id=None, share_type_id=None,
                       client=None, cleanup_in_class=True):
@@ -79,7 +79,7 @@
         metadata = metadata or {}
         kwargs = {
             'share_protocol': share_protocol,
-            'size': size,
+            'size': size or CONF.share.share_size,
             'name': name,
             'snapshot_id': snapshot_id,
             'description': description,