qemuimagetest: fix erroneous ps errors when qemu couldn't be started

The helper script was printing an error to stdout when it couldn't find
any qemu child processes; output this error to stderr instead and
redirect stderr to /dev/null when running from qemuimage-testlib so that
QEMUPID is actually blank if there are no qemu instances found.

(From OE-Core rev: 7c2137a07cca8e1d40d3c8b4b2c6321d80f2b1de)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/qemuimage-testlib

@@ -420,7 +420,7 @@ Test_Create_Qemu()
 
 	while [ ${up_time} -lt 10 ]
 	do
-		QEMUPID=`qemuimage-testlib-pythonhelper --findqemu $XTERMPID`
+		QEMUPID=`qemuimage-testlib-pythonhelper --findqemu $XTERMPID 2>/dev/null`
 		if [ $? -ne 0 ]; then
 			Test_Info "Wait for qemu up..."
 			up_time=`expr $up_time + 5`

scripts/qemuimage-testlib-pythonhelper

@@ -34,7 +34,7 @@ if options.findqemu:
         commands[data[0]] = data[2]
 
     if options.findqemu not in pids:
-        print "No children found matching %s" % options.findqemu
+        sys.stderr.write("No children found matching %s" % options.findqemu)
         sys.exit(1)
 
     parents = []