security_dac: Allow selective remember/recall for chardevs

security_dac: Allow selective remember/recall for chardevs

While in most cases we want to remember/recall label for a
chardev, there are some special ones (like /dev/tpm0) where we
don't want to remember the seclabel nor recall it. See next
commit for rationale behind.

While the easiest way to implement this would be to just add new
argument to virSecurityDACSetChardevLabel() this one is also a
callback for virSecurityManagerSetChardevLabel() and thus has
more or less stable set of arguments. Therefore, the current
virSecurityDACSetChardevLabel() is renamed to
virSecurityDACSetChardevLabelHelper() and the original function
is set to call the new one.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Cole Robinson <crobinso@redhat.com>