implement hubd support for external volatile directories

:Release Notes:
support reading role & service files from USB device

:Detailed Notes:
support reading role & service files from USB device
volatile-dir-control.py implemented to add/remove Volatile Directories

:Testing Performed:
Built and checked that python script works well has 700 permissions set
and ls-control scan-volatile-dirs succeed and ls-hubd is up after that.

:QA Notes:

:Issues Addressed:
[ANG-2981] support reading role & service files from USB device
[BHV-4336] support reading role & service files from USB device
[BHV-4678] Add python dependency to luna-service.bb

Open-webOS-DCO-1.0-Signed-off-by: Sergiy Kryvonos <sergiy.kryvonos@lge.com>

Change-Id: I128735d1989947010b107fa2f211393314a47ea6
Reviewed-on: https://g2g.palm.com/5244
Reviewed-by: DCO Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>