Change gcstress runtest option

No longer passes down SS as the collector. Motivation is to allow
running gcstress with concurrent copying.

New usage is for SS:
mm test-art-host ART_TEST_GC_STRESS=true ART_DEFAULT_GC_TYPE=SS

Bug: 30807718

Test: mm test-art-host ART_TEST_GC_STRESS=true ART_DEFAULT_GC_TYPE=SS

Change-Id: I4416c1ca9ead027536acc9d24b1ec80d5a68c6a1
diff --git a/test/run-test b/test/run-test
index 621fc24..4c29420 100755
--- a/test/run-test
+++ b/test/run-test
@@ -399,7 +399,7 @@
   run_args="${run_args} --runtime-option -Xgc:preverify_rosalloc --runtime-option -Xgc:postverify_rosalloc"
 fi
 if [ "$gc_stress" = "true" ]; then
-  run_args="${run_args} --gc-stress --runtime-option -Xgc:SS,gcstress --runtime-option -Xms2m --runtime-option -Xmx16m"
+  run_args="${run_args} --gc-stress --runtime-option -Xgc:gcstress --runtime-option -Xms2m --runtime-option -Xmx16m"
 fi
 if [ "$trace" = "true" ]; then
     run_args="${run_args} --runtime-option -Xmethod-trace --runtime-option -Xmethod-trace-file-size:2000000"