Several improvements of the lint script.

Report missing python packages, inform about false positives, fail
gracefully if pylint isn't installed. Fixed a bug in the ignore
list and added few more files/directories to it.

ticket 1184

ipalib/cli.py

@@ -33,6 +33,7 @@ import termios
 import struct
 import base64
 try:
+    #pylint: disable=F0401
     import default_encoding_utf8
 except ImportError:
     # This is a chicken-and-egg problem. The api can't be imported unless