All backingStore XML definitions have a XML tag with the timestamp. This
timestamp is not defined insinde RNG volume storage schema and it is
causing some problems to validate and check volume XMLs.
https://bugzilla.redhat.com/show_bug.cgi?id=1594266
Signed-off-by: Julio Faracco <jcfaracco@gmail.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>