qapi: Prefer single-quoted strings more consistently

PEP 8 advises:

    In Python, single-quoted strings and double-quoted strings are the
    same.  This PEP does not make a recommendation for this.  Pick a
    rule and stick to it.  When a string contains single or double
    quote characters, however, use the other one to avoid backslashes
    in the string.  It improves readability.

The QAPI generators succeed at picking a rule, but fail at sticking to
it.  Convert a bunch of double-quoted strings to single-quoted ones.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <1489582656-31133-20-git-send-email-armbru@redhat.com>
diff --git a/scripts/qapi-introspect.py b/scripts/qapi-introspect.py
index fb72c61..032bcea 100644
--- a/scripts/qapi-introspect.py
+++ b/scripts/qapi-introspect.py
@@ -170,10 +170,10 @@
 opt_unmask = False
 
 (input_file, output_dir, do_c, do_h, prefix, opts) = \
-    parse_command_line("u", ["unmask-non-abi-names"])
+    parse_command_line('u', ['unmask-non-abi-names'])
 
 for o, a in opts:
-    if o in ("-u", "--unmask-non-abi-names"):
+    if o in ('-u', '--unmask-non-abi-names'):
         opt_unmask = True
 
 c_comment = '''