added new exception cinderclient.ConnectionError

Introduced new exception cinderclient.ConnectionError
with the change  I37da522e812286e72706409b8a6d4652515f720f.

Adding the exception cinderclient.ConnectionError to the
RECOVERABLE list solves the issues described in the
bug ##1207635.

fixes bug #1207635

Change-Id: I6b90343e79433fe554d84df1db65e096c8ed4423
Merge "added new exception cinderclient.ConnectionError"