cephadm/tests: mock find_program in test_container_engine

cephadm/tests: mock find_program in test_container_engine

test_container_engine mocks find_executable to keep command_check_host
off the real host, but command_check_host looks up 'lvcreate' (and
'systemctl') through find_program, which isn't mocked. So the test
actually needs lvcreate installed and only passes where it is.

Mock find_program too so the test doesn't depend on host binaries.

Signed-off-by: Sun Yuechi <sunyuechi@iscas.ac.cn>