entitymap: add json file loading if present

Step 3 to handle the entity-map transition from YAML to JSON.  This
patchset adds a method that will process the json file, if present to
build the map.

Tested: This patchset has not been tested.
Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I79297aef59844a21f20c0a77de7a21264e2ed96a
2 files changed