Add test_com.android.server apex for e2e tests.

The test apex contains a single FakeApexSystemService that just logs to
logcat in onStart(). The host test would parse logcat to check whether
the apex-system-service has been started correctly or not.

Bug: 192880996
Test: presubmit
Ignore-AOSP-First: tests depend on new internal feature
Change-Id: Ia3630510306aee2b5596e57abba6b1163dd84309