This commit is the result of the squash of the following main commits:

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Tue Jul 21 10:28:13 2020 +0200

    regress: Add copyright to regress scripts

Author: Alain Spineux <alain@baculasystems.com>
Date:   Tue Aug 28 13:55:46 2018 +0200

    regress: adjust snapshots tests to new snapshot (dual path)

    - for LVM, if no VG exists create a loopback device to do the job
    - tweak "grep" to adjust the dual path change
    - btrfs is not working yet

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Fri Mar 20 09:22:03 2015 +0100

    regress: Tweak snapshot tests for new trace output

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Sun Mar 8 09:44:04 2015 +0100

    snapshot: Call support() only if the device is in the fileset

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Sat Mar 7 10:05:29 2015 +0100

    regress: Add symlinks to snapshot test

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Fri Feb 20 17:11:14 2015 +0100

    snapshot: More work on LVM backend and on list/sync commands

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Wed Feb 18 10:21:46 2015 +0100

    regress: use bsnapshot.conf in regress tests

Author: Eric Bollengier <eric@baculasystems.com>
Date:   Thu Feb 5 09:42:01 2015 +0100

    Add Snapshot Engine to bacula core

            Rename jcr->VSS to jcr->Snapshot and use the same variable on Linux/Windows
            Pass snapshot retention to the FD
            Add SnapshotRetention to client and job resource
            Add documentation about snapshot backend
            regress: Add snapshot script for lvm backend
            Use retry in lvm unmount procedure
            Read config file from sysconfigdir
            Load bsnapshot.cfg by default and configure bsnapshot using exepath
            Add config file to specify lvm snapshot parameters
            Control LVM free space for snapshot
            Implement OT_PINT64 in output writer, should display job speed api2 mode status command
            regress: Add test to test snapshot bconsole commands
            regress: Add test for zfs snapshot
            implement zfs driver (linux zfs driver cannot mount snapshots)
            regress: Add regress script for snapshots
            Include automatically subvolumes with onefs=no
            Handle ff->link in strip snapshot path
            Scan for subvolumes not listed in mtab
            Snapshots can be created/deleted from the catalog
            Implement path translation between snapshot
            Add JobId to Snapshot table
            Add code to execute snapshot script on the FD side
            Add more Director snapshots command
            Implement CatReq interface for Snapshots
            Implement DB snapshot functions
            the delete snapshot is now connecting to the FD, and the
            FD is calling the snapshot script with the delete argument
            Allow to specify env variable in run_command_full_output() and open_bpipe()
            Modify cmd_parser to not look for plugin name with use_name option
            Add ARG_LIST to generate nice arg1=arg2 output from db_list function
            Add tag DT_SNAPSHOT
            Add JobId in the list snapshot output
            Add list snapshot command
            Add JobId to snapshot table