Whitelist commonly variable names

Some variable names are so common, that it is more confusing not to use
them, although they are short.

This change adds `fd` and `ax`.

Change-Id: Ibe9b8425df106d51fffe2e2ecad81a5a943c801e

pylintrc

@@ -106,7 +106,7 @@ evaluation=10.0 - ((float(5 * error + warning + refactor + convention) / stateme
 [BASIC]
 
 # Good variable names which should always be accepted, separated by a comma
-good-names=i,j,k,ex,Run,_
+good-names=i,j,k,ex,Run,_,ax,fd
 
 # Bad variable names which should always be refused, separated by a comma
 bad-names=foo,bar,baz,toto,tutu,tata,I,l,O