oeqa/core/runner.py: OEStreamLogger fix logging

Change conditional to avoid losing stack traces when log
into the logger. The logic only needs to don't log empty lines.

(From OE-Core rev: 545dd180cc27a69732f2332565038bd06d01c014)

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/core/runner.py

@@ -23,7 +23,7 @@ class OEStreamLogger(object):
         self.buffer = ""
 
     def write(self, msg):
-        if msg[-1] != '\n':
+        if len(msg) > 1 and msg[0] != '\n':
             self.buffer += msg
         else:
             self.logger.log(logging.INFO, self.buffer.rstrip("\n"))