Add dedicated URL for issuing unscoped federation tokens.

Add URL /v3/OS-FEDERATION/identity_providers/{identity_providers}/
protocols/{protocols}/auth that can be later used as a protected
endpoint in mod_shib configuration.
Client should be able to access this URL with a HTTP GET and POST
methods, passing the information about the identity provider as well
as protocol in the URL.

Change-Id: Ib6c6bc761f73844e1fc5fd7c606c7a5573077b6b
Closes-Bug: #1296348
Always include 'enabled' field in service response

NOTE: this is basically a mirror of the following patch, but for
services instead of endpoints:

    https://review.openstack.org/#/c/75727/

The 'enabled' field wasn't always returned in a service response.

The 'enabled' attribute for services was stored in the 'extra'
column as part of a JSON string. Now the 'enabled' attribute is in
its own column. It will also be easier to filter out disabled
services now that enabled is a separate column.

With the 'enabled' field being a Boolean column in the database,
the server also needs to validate that the value is a Boolean (if
it's present). This is done in the same way that the server checks
the type of the 'enabled' value when creating users.

Change-Id: I73f0bb58cd31d80b3c1b6c6834e9e8b38adc86a0
Co-Authored-By: Brant Knudson <bknudson@us.ibm.com>
Partial-Bug: 1273867
Merge "Add dedicated URL for issuing unscoped federation tokens."
Merge "Always include 'enabled' field in service response"