Added missing default message in InvalidCredentials exception
Added missing default message in InvalidCredentials exception

Fixes bug #1255623

Change-Id: I42edbebc1df3aa68bb29d0144b3e57484b13164b

redhat-openstack/sahara,zhujzhuo/Sahara,xme1226/sahara,henaras/sahara,redhat-openstack/sahara,esikachev/sahara-backup,openstack/sahara,crobby/sahara,egafford/sahara,mapr/sahara,redhat-openstack/sahara,ekasitk/sahara,mapr/sahara,crobby/sahara,henaras/sahara,mapr/sahara,bigfootproject/sahara,xme1226/sahara,openstack/sahara,esikachev/scenario,keedio/sahara,henaras/sahara,zhangjunli177/sahara,bigfootproject/sahara,ekasitk/sahara,egafford/sahara,zhujzhuo/Sahara,keedio/sahara,xme1226/sahara,crobby/sahara,matips/iosr-2015,tellesnobrega/sahara,tellesnobrega/storm_plugin,tellesnobrega/storm_plugin,tellesnobrega/sahara,esikachev/scenario,zhujzhuo/Sahara,citrix-openstack-build/sahara,zhangjunli177/sahara,matips/iosr-2015,keedio/sahara,esikachev/sahara-backup,matips/iosr-2015,citrix-openstack-build/sahara,ekasitk/sahara,tellesnobrega/storm_plugin,zhangjunli177/sahara,esikachev/scenario,bigfootproject/sahara,citrix-openstack-build/sahara,esikachev/sahara-backup