RFR: Enable ShenandoahEvacReserveOverflow by default

[Aleksey Shipilev]

Some of weekend tests feel much better with evac-reserve overflows allowed. Let's make that the default:

diff -r f8f9c1f0f62b src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp
--- a/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp    Sat Sep 01 17:09:56 2018 +0200
+++ b/src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp    Mon Sep 03 11:07:17 2018 +0200
@@ -202,10 +202,9 @@
           range(1,100)                                                      \
                                                                             \
-  experimental(bool, ShenandoahEvacReserveOverflow, false,                  \
+  experimental(bool, ShenandoahEvacReserveOverflow, true,                   \
                "Allow evacuations to overflow the reserved space. "         \
                "Enabling it will make evacuations more resilient when "     \
                "evacuation reserve/waste is incorrect, at the risk that "   \
-               "application allocations run out of memory too early. "      \
-               "This is safe to enable when pacing is disabled.")           \
+               "application allocations run out of memory too early.")      \
                                                                             \
   experimental(uintx, ShenandoahImmediateThreshold, 90,                     \

Testing: tier1_gc_shenandoah, ad-hoc benchmarks

Thanks,
-Aleksey