Add support for the System erase_partition method

:Release Notes:
`nyx-cmd System erase_parition` can now be used to remove the firstmount
file from various read-write partitions.

:Detailed Notes:
Factory Reset requires that various locations in the writable partitions
be marked for erasure on the next reboot. Each of these partitions will
then be reset to their initial states.

This commit adds support for invoking the `nyx_system_erase_parition()`
method that marks the paritions for erasure.

:Testing Performed:
- Local build created and installed
- Various forms of `nyx-cmd System erase_partition` executed.
- The partitions were examined to ensure they were marked correctly.
- Ensured that invalid command lines were handled appropriately.

:QA Notes:

:Issues Addressed:
[GF-138]   User can reset the device to factory settings.
[GF-37730] Provide nyx-modules-lg implmentation of system module to support factory reset

Open-webOS-DCO-1.0-Signed-off-by: Keith Derrick <keith.derrick@lge.com>

Change-Id: Iec3fe0f54889ca61392f4e65c6b39ca9c3690227
Reviewed-on: https://g2g.palm.com/3541
Reviewed-by: Build Verification
Reviewed-by: Keith Derrick <keith.derrick@lge.com>
Tested-by: Keith Derrick <keith.derrick@lge.com>