Exit HostConnection for thread which only uses gralloc

For certain guest process which maintains a thread pool and only calls gralloc
library, we should exit the host connection to avoid spawning too many
render threads on host emulator.

Test: run empty test activity for 3000 times and the number of render
thread on host should stay roughly the same.
BUG: 80050618

Change-Id: Idb282aa67138572519edee761f8bc6cb50c1653d
Signed-off-by: Weilun Du <wdu@google.com>
(cherry picked from commit 904b90eb097609762c7c35c321f82b2cc5245190)