contrib: fix python warnings for oe-stylize

I get a couple of python SyntaxWarnings when running oe-stylize:

  [jk@pecola meta-openembedded]$ python3 contrib/oe-stylize.py
  contrib/oe-stylize.py:372: SyntaxWarning: "is not" with a literal. Did you mean "!="?
    if line is not '':
  contrib/oe-stylize.py:389: SyntaxWarning: "is" with a literal. Did you mean "=="?
    if line.isspace() or line is '':

The 'is' operator is for object reference comparison, which is not what
we want here. Change to '==' / '!=' instead.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

contrib/oe-stylize.py

@@ -369,7 +369,7 @@ if __name__ == "__main__":
             line = line.expandtabs().rstrip()
             # ignore empty lines (or line filled with spaces or tabs only)
             # so that rule6 is always respected
-            if line is not '':
+            if line != '':
                 lines.append(line)
 
     # -- parse the file --
@@ -386,7 +386,7 @@ if __name__ == "__main__":
         line = follow_rule(6, line)
 
         # ignore empty lines
-        if line.isspace() or line is '':
+        if line.isspace() or line == '':
             # flush comments into the olines
             for c in commentBloc:
                 olines.append(c)