Mock auth_end_time in test_shell.test_download
Mock auth_end_time in test_shell.test_download

If we don't we are getting an error like this under py3:

TypeError: unsupported operand type(s) for /: 'float' and 'MagicMock'

Change-Id: If5a6947757297354e6b81fc45f011cc2921d609f

jeseem/python-swiftclient,pratikmallya/python-swiftclient,varunarya10/python-swiftclient,openstack/python-swiftclient,krnflake/python-hubicclient,VyacheslavHashov/python-swiftclient,JioCloud/python-swiftclient,VyacheslavHashov/python-swiftclient,jeseem/python-swiftclient,varunarya10/python-swiftclient,iostackproject/IO-Bandwidth-Differentiation-Client,iostackproject/IO-Bandwidth-Differentiation-Client,ironsmile/python-swiftclient,JioCloud/python-swiftclient,sohonetlabs/python-swiftclient,openstack/python-swiftclient,pratikmallya/python-swiftclient,sohonetlabs/python-swiftclient,ironsmile/python-swiftclient