Fix DictOpt support in config sample generator

Class DictOpt was defined in oslo.config.cfg .
The config sample generator cannot recognize DictOpt type config options,
and will exit with exception when generating config sample files from codes
that contain DictOpt type options. This will result in unexpected output
of tools/config/generate_sample.sh and tools/config/check_uptodate.sh.
This problem is fixed by adding DictOpt support to config sample generator.

Change-Id: Ia360dbfae8446ddaa563e94f51900071e95cdf6d
Closes: bug #1276859
Remove None for dict.get()

Because If no default value is specified it defaults to None already.

Change-Id: Iebbb0622f7941c6ce8ea26aca1968f1ae68a6c14
Merge "Fix DictOpt support in config sample generator"
Merge "Remove None for dict.get()"