Config: change cinder bootable flag to True.

This flag was not supported by ice-house .

The change will allow to run tests related to bootable flag

Change-Id: Ib16afc288d661dbf468447a43bcfbf323c959936
diff --git a/tempest/config.py b/tempest/config.py
index 0cda018..e31bfb7 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -765,9 +765,10 @@
                 default=True,
                 help="Is the v2 volume API enabled"),
     cfg.BoolOpt('bootable',
-                default=False,
+                default=True,
                 help='Update bootable status of a volume '
-                     'Not implemented on icehouse ')
+                     'Not implemented on icehouse ',
+                deprecated_for_removal=True)
 ]