remove hardcoding for allowed_schemas parameter of urlfetch.get

[SnowDust]

https://github.com/openstack/heat/blob/master/heat/common/urlfetch.py#L37

the allowed_schemas parameter should be based on configuration defaults and not hardcoded in the function itself. This allows the override of allowed_schemes using heat configuration.

[Openstack Gerrit (openstack-gerrit)]

Fix proposed to branch: master
Review: https://review.openstack.org/88659

[Thomas Herve (therve)]

I don't think it's a good idea, until a proper use case is shown.

[SnowDust (nilakhya-chatterjee)]

discussing this with community it appears that the bugfix referenced is a security issue(therve said so) and no change is needed.