Description of problem:

CFME returns errors when creating the Foreman or AnsibleTower providers based on the documented sample https://github.com/ManageIQ/manageiq_docs/blob/master/api/reference/providers.adoc#foreman-support

Version-Release number of selected component (if applicable):
CFME 5.6.2.2.20161017185613_7cee0a0 

How reproducible:
100%

Steps to Reproduce:
1. Use curl to POST the sample json structure to cfme provider api endpoint
2. Vary the json structure to include/exclude the URL parameter
3.


Actual results:

# curl -k  -u admin:XXXXX -d '{
  "type"      : "ManageIQ::Providers::Foreman::Provider",
  "name"      : "new_foreman_111",
  "url"       : "100.200.300.111",
  "credentials" : {
    "userid"   : "foreman_admin",
    "password" : "foreman_password"
  }
}' https://localhost/api/providers?provider_class=provider
{"error":{"kind":"bad_request","message":"Could not create the new provider - Invalid Provider attributes url specified","klass":"ApiController::BadRequestError"}}

# curl -k  -u admin:redhat01 -d '{
  "type"      : "ManageIQ::Providers::Foreman::Provider",
  "name"      : "new_foreman_111",
  "credentials" : {
    "userid"   : "foreman_admin",
    "password" : "foreman_password"
  }
}' https://localhost/api/providers?provider_class=provider
{"error":{"kind":"bad_request","message":"Could not create the new provider - Validation failed: Url can't be blank","klass":"ApiController::BadRequestError"}}


Expected results:
Provider is created, summary is returned


Additional info:

Same also applies to the AnsibleTower provider

This check does seem to flag "url" as an invalid parameter:
https://github.com/ManageIQ/manageiq/blob/master/app/controllers/api/providers_controller.rb#L193