python: Add 'fh' to known-good variable names

fd and fh are fine: we often use these for "file descriptor" or "file
handle" accordingly. It is rarely the case that you need to enforce a
more semantically meaningful name beyond "This is the file we are using
right now."

While we're here: add comments for all of the non-standard pylint
names. (And the underscore.)

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210603003719.1321369-10-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/setup.cfg

@@ -78,9 +78,10 @@ good-names=i,
            k,
            ex,
            Run,
-           _,
-           fd,
-           c,
+           _,   # By convention: Unused variable
+           fh,  # fh = open(...)
+           fd,  # fd = os.open(...)
+           c,   # for c in string: ...
 
 [pylint.similarities]
 # Ignore imports when computing similarities.