Add ls-method to make backup file for /var/log

:Release Notes:
Add ls-method to make backup file for /var/log
Initialize some variables.

:Detailed Notes:
"backuplogs" added as a new ls-method that can create tarball which
is backup file for /var/log.
This method should be called when system is going to shutdown to
provide to developer can check their log files after rebooting.
That backup file will be located at "/var/spool/rdxd"
which is non-volatile memory.
And the file will not be accumulated on every reboot or shutdown.
There is only one "previous_boot_logs.tar.gz" file.

:Testing Performed:
Compiled locally and tested on a device.

:QA Notes:

:Issues Addressed:
[GF-43166] Add ls-method that can create backup file for /var/log
           to PmLogDaemon

Open-webOS-DCO-1.0-Signed-off-by: Hongjeon Ha <hj.ha@lge.com>

Change-Id: I840c1021c3bf165cf80689a508ca6064f5215157
Reviewed-on: https://g2g.palm.com/3704
Reviewed-by: Build Verification
Reviewed-by: Hongjeon Ha <hj.ha@lge.com>
Tested-by: Hongjeon Ha <hj.ha@lge.com>
Reviewed-by: Keith Derrick <keith.derrick@lge.com>