storage_source: Add field for skipping seclabel remembering

storage_source: Add field for skipping seclabel remembering

In case of incoming migration where a local directory is shared to other
hosts we'll need to avoid seclabel remembering as the code would
remember the seclabel already allowing access to the image.

As the decision requires a lot of information not available in the
security driver it would either require plumbing in unpleasant callbacks
able to pass in the data or alternatively we can mark this in the
'virStorageSource' struct.

This patch chose to do the latter approach by adding a field called
'seclabelSkipRemember' which will be filled before starting the process
in cases when it will be required.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>