improve error handling for userscripts

from python-diamond/Diamond#536

Author: shawnbutts

src/collectors/userscripts/userscripts.py

@@ -76,22 +76,23 @@ def collect(self):
                                (absolutescriptpath, e))
                 continue
             if proc.returncode:
-                self.log.error("%s return exit value %s; skipping" %
+                self.log.error("%s return exit value %s" %
                                (absolutescriptpath, proc.returncode))
+            if err:
+                self.log.warning("%s return error output: %s" %
+                                 (absolutescriptpath, err))
             if not out:
-                self.log.info("%s return no output" % absolutescriptpath)
+                self.log.error("%s returned no output; skipping" %
+                               absolutescriptpath)
                 continue
-            if err:
-                self.log.error("%s returned error output (stderr): %s" %
-                               (absolutescriptpath, err))
             # Use filter to remove empty lines of output
             for line in filter(None, out.split('\n')):
                 # Ignore invalid lines
                 try:
                     name, value = line.split()
                     float(value)
                 except ValueError:
-                    self.log.error("%s returned invalid/unparsable output: %s" %
+                    self.log.error("%s returned error output: %s" %
                                    (absolutescriptpath, line))
                     continue
                 name, value = line.split()