Bugfix: openrc api dump should be safe_dump

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>
(cherry picked from commit f1a71b2889da3b49358b10b9a12ea5a512dd2743)