Fixed mn ping command not working with tagged hosts

When using command `mn> hi ping h2`, if h2 was a tagged host, Mininet
was unable of getting the IP address of h2

Change-Id: I4a557b8c81ee1f080edf6b4ebfbf25385eef08f6
diff --git a/.gitignore b/.gitignore
index 80e400d..6bbaf2c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 *.pyc
 *.project
 *.pydevproject
+.idea
 
 # vagrant
 trellis/.vagrant/