!! handle the Jmsg at an upper level when required

!! handle the Jmsg at an upper level when required

The goal is to allow the "next_volume" to work in a backup and in last
resort to finish by a mount request

This Jmsg was handy, it was avoiding to handle the error a the caller level
and sometime at the caller+2 level
Here they are

DEVICE::load_encryption_key(DCR *, const char *, const char *, u_int32_t *, unsigned char *, u_int32_t *, unsigned char *) : bool
	DEVICE::read_dev_volume_label(DCR *) : int
		acquire_device_for_read(DCR *, u_int32_t) : bool
		aligned_dev::read_dev_volume_label(DCR *) : int
		cloud_dev::read_dev_volume_label(DCR *) : int
		DCR::check_volume_label(bool &, bool &) : int
		device_initialization(void *) : void *
		label_volume_if_ok(DCR *, char *, char *, char *, int, int) : void
		mount_cmd(JCR *) : bool
		read_label(DCR *) : bool
		read_volume_label(JCR *, DCR *, DEVICE *, int) : void
		readlabelcmd() : void
	DEVICE::rewrite_volume_label(DCR *, bool) : bool
		cloud_dev::rewrite_volume_label(DCR *, bool) : bool
		DCR::mount_next_write_volume() : bool
	DEVICE::write_volume_label(DCR *, const char *, const char *, bool, bool) : bool
		cloud_dev::write_volume_label(DCR *, const char *, const char *, bool, bool) : bool
		DCR::try_autolabel(bool) : int
		label_volume_if_ok(DCR *, char *, char *, char *, int, int) : void
		labelcmd() : void