Deoptimize zygote compiled methods in DeoptimizeBootImage.

Those methods don't get compiled with the "debuggable" flag,
so we need to deoptimize them.

Also fix a bug revealed by the new test where a concurrent
JIT collection happens when trying to disable it.

Also make DeoptimizeBootImage truly mutator lock exclusive.

Test: 689-zygote-jit-deopt
Change-Id: I00607dbe100350c5328293c35c87946fa97924b8