Update Pure REST API supported version numbers in Pure driver
Update Pure REST API supported version numbers in Pure driver

Add 1.5 as a supported REST API version for the driver in general and for the
snap management code required version numbers.

REST API v1.5 is available in Purity versions >= 4.6.0

Change-Id: Id509b0b59843d13ce1a1925809190121da296ef9
Closes-Bug: 1524434

NetApp/cinder,Hybrid-Cloud/cinder,eharney/cinder,ge0rgi/cinder,mahak/cinder,Datera/cinder,j-griffith/cinder,Datera/cinder,dims/cinder,phenoxim/cinder,openstack/cinder,mahak/cinder,j-griffith/cinder,bswartz/cinder,dims/cinder,Hybrid-Cloud/cinder,Nexenta/cinder,eharney/cinder,openstack/cinder,Nexenta/cinder,cloudbase/cinder,cloudbase/cinder,phenoxim/cinder,bswartz/cinder,NetApp/cinder