Fixes bug #1044090
hasManagedSaveImage is not implmented in the LXC libvirt driver, resulting
in the following error when a vm is deleted "Error from libvirt during saved
instance removal. Code=3 Error=this function is not supported by the
connection driver: virDomainHasManagedSaveImage"
This commit replaces the use of hasManagedSaveImage, managedSaveRemove and
undefine with undefineFlags which does the work of all 3 calls and is
implemented in versions of libvirt > 0.9.4. We also revert back to calling
undefine if undefineFlags raises an error.
Change-Id: Ib8d451aeff7767f835c3c1aab99ee4ab5e299852