Create and add permission for persist_bms_file

libhealthd.msm needs access to write some battery parameters to
a file in /persist. File will be created under /persist/bms. Add
persist_bms_file and provide healthd access to it.

CRs-Fixed: 1018233
Change-Id: I805084f6e9d729b6b0e36a751964e729e01799e5