Break execution order dependency between tests

In WebsocketControllerTest, testCredentials relied on one of the mock
setups from testOpen. This meant testCredentials could only be run
successfully after testOpen. This commit moves the mock setup into an
@Before method and removes the static qualifier from the mock fields
so each test now runs independently.
Fix test some assertion in KeyControllerTest to actually assert

The former assertThat(value == 4) was not actually performing an
assertion since there was no .isEqualTo or .isTrue()
Have sample device return sample signed key to make test assertion pass