Replace native Process getpid/getuid with calls to libcore equivalents.

The Process natives were getting called were getting called while
handling a jdwp packet before the vm had a chance to register them.

(cherry-pick of 5bce6a308fc8a3c1e449cf905b8b6e8ace4ef3e2.)

Change-Id: Ia2b4f79b11e427283a712b2d0c52948f394640bf