Bugfix: openrc api dump should be safe_dump
1. fix safe_dump
2. fix pep8 problem, use flask_restapi custom error handling [1]
[1] https://flask-restful.readthedocs.io/en/latest/extending.html#custom-error-handlers
JIRA: YARDSTICK-1165
RestApi openrc dump clouds.yaml error
it now use yarml.dump, should be yaml.safe_dump.
dump would gererate !!python/unicode and cause error when upload openrc file in gui
Change-Id: Id3e85f7ba7d4967277ef79109b07d7552179e5db
Signed-off-by: rexlee8776 <limingjiang@huawei.com>