frameworks/base : testNoManagedUsersIfLowRamDevice failure

Issue : testNoManagedUsersIfLowRamDevice verifies whether the
managed_users feature is disabled on low ram devices. Currently
the feature is enabled for all targets irrespective of RAM size

Fix : Sysconfig populates the preconfigured list of features
from handheld_core_hardware.xml.A check is added during parsing
of the xml to avoid adding managed_users feature on low ram devices.

CRs-Fixed: 776709

Change-Id: Ib0448d6c39cccbe0567d3ad50b27c93ad5dd9618