RFR [8u]: Bulk backports to sh/jdk8

[Aleksey Shipilev]

This backports a few things to sh/jdk8u:
 [backport] 8217043: Shenandoah: SIGSEGV in Type::meet_helper() at barrier expansion time
 [backport] 8222843: Print Shenandoah cset map addresses in hs_err
 [backport] 8222838: Shenandoah: SEGV on accessing cset bitmap for NULL ptr
 [backport] 8220712: [TESTBUG] gc/shenandoah/compiler/TestMaybeNullUnsafeAccess should run with ...
 [backport] 8222130: Shenandoah should verify roots after pre-evacuation
 [backport] 8222185: Shenandoah should report "committed" as capacity
 [backport] 8222186: Shenandoah should not uncommit below minimum heap size

Webrev:
  http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20190426/webrev.01/

Testing: hotspot_gc_shenandoah {fastdebug,release}

-- 
Thanks,
-Aleksey