Tune JVM, print full diagnostics on crash.

JVM occasionally (0.5% time) crashes on entering a method with SIGSEGV.
It might be due to excessive load on the host machine. Reduce the number
of the compiler threads to 6, and do not start all the GC threads
immediately. If JVM crashes, copy full diagnostics to stderr.

Bug: 132766811
Test: treehugger
Change-Id: Ib7bfd568f6d32456bf623cbb615ffc990c326a34