block: Generically refresh runtime options

Instead of having every block driver which implements
bdrv_refresh_filename() copy all of the strong runtime options over to
bs->full_open_options, implement this process generically in
bdrv_refresh_filename().

This patch only adds this new generic implementation, it does not remove
the old functionality. This is done in a follow-up patch.

With this patch, some superfluous information (that should never have
been there) may be removed from some JSON filenames, as can be seen in
the change to iotests 110's and 228's reference outputs.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190201192935.18394-24-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>