Include ahat in the general-tests tradefed suite.

Specifically, this makes ahat available on the classpath of the
general-tests tradefed suite. It will be used by libcore tests that
run there.

Change-Id: If3fa3a78c6b9c4ce4df22305bcd8d731b9466671
Bug: 67283029
Bug: 67999970
Test: make ahat tradefed-all