misc_info: Add factory script location to misc_info when available

When a factory script is specified for the device, store the location
of the script in the misc_info package for proper use during package
signing.

Change-Id: Icd3ab59ebb68b8b6c92aff8eaf9e44322cdcbc18
Ticket: RM-112
(cherry picked from commit 8356ec9c)