Allow multiple mkbackuponly or restoreonly running in parallel

[jsmeix]

New SIMULTANEOUS_RUNNABLE_WORKFLOWS variable
lists those workflows that are allowed to run simultaneously
but cannot use LOGFILE.lockless as the LOCKLESS_WORKFLOWS.
Instead the SIMULTANEOUS_RUNNABLE_WORKFLOWS
get a LOGFILE with PID because simultaneously runnable
workflows require unique logfile names, see
#1102

Additional enhancements and fixes in usr/sbin/rear:

CONFIG_APPEND_FILES that are not in CONFIG_DIR
get added to COPY_AS_IS to get them copied into the
recovery system.

Moved progress subsystem enablement
(i.e. source $SHARE_DIR/lib/progresssubsystem.nosh)
and enablement of debug output of the progress pipe
after the user config files had been read, because
otherwise a PROGRESS_MODE setting in a
user config file is not used when defining the
progress functions inprogresssubsystem.nosh

[jsmeix]

With that changes
"Multiple simultaneous backups and/or restores"
work well for me.