Add multiple filesystem path support for backup and restore

Freezer needs to be able to execute backups when providing multiple paths for backups and restores (i.e. /var/lib/mysql /etc/apache2 /var/log).

Implementation thoughts:
The argument/option: --backup-fom-path can take multiple comma separated path

Currently Freezer execute the backup by changing the CWD to the directory where the data to back up is. This behavior needs to be changed as the backups should be executed as absolutes paths (i.e. tar needs the -P option to keep the leading /'

Same apply for the restore:

--restore-abs-path opt/arg would be redundant, as the data would be backed up on the same file system path where the data was located, when the backup was executed.

Another issue would the lvm snapshot to create, in case the multiple provided path resides on different lvm volumes. This needs to be carefully analyzed. A possible solution would be to create volume snapshot only to the file path provided by --lvm-auto-snap or specifically set by command line. All other directories/files backups will be done without lvm snapshot.