Properly log verifier exceptions.

If an exception is thrown in the verifier child process for a
specific exchange, log it properly.

Was simply printing to stdout, which goes nowhere for daemon processes.

Change-Id: I528ad08e70d7bdf03e9a8e1d8abe45d09f2eb476

verifier/base_verifier.py

@@ -211,10 +211,13 @@ class Verifier(object):
                 try:
                     self._run(callback=callback)
                 except Exception, e:
-                    print e
-                    raise e
+                    msg = "ERROR during Verification %s: %s" % (exchange_name,
+                                                                e)
+                    logger.exception(msg)
+                    return True
         else:
             self._run()
+        return False
 
     def verify_for_range(self, ending_max, callback=None):
         pass