untrusted_apps: Allow untrusted apps to find healthd_service.

This allows apps to find the healthd service which is used to query
battery properties.

Bug: 24759218
Change-Id: I72ce5a28b2ffd57aa424faeb2d039b6c92f9597d
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>