Add a test to verify a process killed by lmkd is being reaped when
kernel supports process_mrelease syscall.
Bug: 203597692
Test: atest LmkdTest
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Iac46f68c811e6e89378952ce1d29daf8a47514e2