Correct the wrong ":guilabel:" markup value
Correct the wrong ":guilabel:" markup value

There should be "Edit Image" dialog box and should be "Edit Image" button,
not "Update Image". This patch fix them.

Change-Id: Ibc0a3f5610a3f7765296b1b71ec44936fcb3834b
Closes-Bug: #1615660

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals