Print & log messages on scriptlet/transaction errors

We should probably let the user know if something goes wrong with the
transaction or if a scriptlet fails. So: log the messages so we can find
(and, one hopes, fix) them later.

src/pylorax/yumhelper.py

@@ -115,3 +115,10 @@ class LoraxRpmCallback(yum.rpmtrans.RPMBaseCallback):
     def filelog(self, package, action):
         if self.fileaction.get(action) == "Installed":
             logger.debug("{0} installed successfully".format(package))
+
+    def errorlog(self, msg):
+        logger.warning("RPM transaction error: %s", msg)
+
+    def scriptout(self, package, msgs):
+        if msgs:
+            logger.info("%s scriptlet output:\n%s", package, msgs)