Print to System.err in test 909 to avoid output races.
Throwable.printStackTrace() prints to System.err, so print
all other output to System.err as well to avoid races like
#################### info
# Tests jvmti plugin attaching during live phase.
#################### diffs
--- expected.txt 2017-01-13 18:22:13.
897224469 +0000
+++ output.txt 2017-01-30 17:51:21.
091550290 +0000
@@ -6,6 +6,6 @@
Goodbye!
Hello, world!
java.io.IOException: Process is not debuggable.
+Goodbye!
at dalvik.system.VMDebug.attachAgent(Native Method)
at Main.main(Main.java:27)
-Goodbye!
####################
Test: m test-art-host-run-test-909-attach-agent
Change-Id: I956bd24db056154b938568c156df80d4ff56ba11