hsm: protect deleteImage with the spm lock

Change-Id: Iac5b4b0f71de6a12de34513d4fafb295b701306c
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19795
Reviewed-by: Dan Kenigsberg <danken@redhat.com>