Fix parse_exception to handle exception from keystoneauth1
Fix parse_exception to handle exception from keystoneauth1

Keystoneauth1 is used by OpenStackSDK, but OpenStackSDk does
not handel the exceptions, senlinclient need to make the exception
more readable.

Change-Id: I17d900af88d4e668b2aabe37ca3f9d0b53e05af3
Closes-bug: #1520464

stackforge/python-senlinclient,openstack/python-senlinclient,stackforge/python-senlinclient,openstack/python-senlinclient