Trivial fix typo: Unavilable to Unavailable
Trivial fix typo: Unavilable to Unavailable

This patch fixes a typo in an exception message.

Change-Id: I204b0bff94970d8743872cd184b8431d30dd1341

wkoathp/glance,takeshineshiro/glance,scripnichenko/glance,ozamiatin/glance,dims/glance,kfwang/Glance-OVA-OVF,openstack/glance,paramite/glance,jumpstarter-io/glance,saeki-masaki/glance,akash1808/glance,kfwang/Glance-OVA-OVF,rajalokan/glance,JioCloud/glance,rajalokan/glance,darren-wang/gl,sigmavirus24/glance,JioCloud/glance,redhat-openstack/glance,klmitch/glance,klmitch/glance,stevelle/glance,vuntz/glance,akash1808/glance,scripnichenko/glance,wkoathp/glance,jumpstarter-io/glance,redhat-openstack/glance,darren-wang/gl,stevelle/glance,ozamiatin/glance,saeki-masaki/glance,paramite/glance,sigmavirus24/glance,openstack/glance,vuntz/glance,dims/glance,openstack/glance,takeshineshiro/glance