Add share_size config option

All tempest tests create shares with fixed size, 1GB. This patch add
a config option in order to allow configurable share sizes as cinder
does (Cinder change-ID reference:
I2897f6d6bd970f73867f56d9d23a768cafcbfd80).

TrivialFix

Change-Id: Ifd09519b63c6c1a0ec8449e5dae1ffe0caa1b879
diff --git a/manila_tempest_tests/tests/api/base.py b/manila_tempest_tests/tests/api/base.py
index cd16c60..21dd2da 100644
--- a/manila_tempest_tests/tests/api/base.py
+++ b/manila_tempest_tests/tests/api/base.py
@@ -349,7 +349,7 @@
         return share_network_id
 
     @classmethod
-    def _create_share(cls, share_protocol=None, size=1, name=None,
+    def _create_share(cls, share_protocol=None, size=None, name=None,
                       snapshot_id=None, description=None, metadata=None,
                       share_network_id=None, share_type_id=None,
                       consistency_group_id=None, client=None,
@@ -358,6 +358,7 @@
         description = description or "Tempest's share"
         share_network_id = share_network_id or client.share_network_id or None
         metadata = metadata or {}
+        size = size or CONF.share.share_size
         kwargs.update({
             'share_protocol': share_protocol,
             'size': size,