Add JVMTI agent to dump/reset JaCoCo coverage information

This agent can be attached to an arbitrary Android process with
arguments that cause it to either reset or dump the JaCoCo information
to a provided directory.

Test: manual, used examples in README to test whether it works on a
userdebug_coverage build on cuttlefish

Change-Id: If6cee20046f790676b8085e1ca84652c063295fa