qemurunner.py: handle getOutput() having nothing to read

(From OE-Core rev: f4abfdeea175cfcadd6f73a69a676632ab4334a6)

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/qemurunner.py

@@ -123,7 +123,10 @@ class QemuRunner:
         import fcntl
         fl = fcntl.fcntl(o, fcntl.F_GETFL)
         fcntl.fcntl(o, fcntl.F_SETFL, fl | os.O_NONBLOCK)
-        return os.read(o.fileno(), 1000000).decode("utf-8")
+        try:
+            return os.read(o.fileno(), 1000000).decode("utf-8")
+        except BlockingIOError:
+            return ""
 
 
     def handleSIGCHLD(self, signum, frame):