Add a unit test for Android Runtime (Boot) device configuration flags.
These flags live in device configuration namespace
`runtime_native_boot`. Exercise them by checking that they are passed
to the zygote process(es) as a runtime option after a reboot.
At the moment this test only checks flag `gctype`, which is the only
flag currently implemented in namespace `runtime_native_boot`.
Test: core/jni/runtime_native_boot-flags-test.sh
Bug:
72446017
Bug:
120794191
Bug:
123524494
Bug:
123754583
Change-Id: I6cf43c3ee0d405fb1b69a450587dd712f911358d