Debug env for tox

Running a test with pdb was difficult because testr captures
output and causes pdb prompt to quit.

Tips for how to run with debug are provided here:
 https://wiki.openstack.org/wiki/Testr#Debugging_.28pdb.29_Tests

This change puts these commands into a debug env in tox.ini so
you can do a command like

 tox -e debug test_v3_trust_token_get_token_fails

or, for more granularity:
 tox -e debug keystone.tests.test_sql_migrate_extensions.EndpointFilterExtension
 tox -e debug keystone.tests.test_sql_migrate_extensions.EndpointFilterExtension.test_downgrade

and when it hits your breakpoint you'll get the debug prompt.

Change-Id: I2b5dc81f4652dc89ecbcc7c785245a81cf77a1ca
Fix errors for create_endpoint api in version2

1. Create an endpoint without 'service_id' should return a 400 Bad Request
with appropriate message instead of 500 Internal Server Error.
2. Empty urls should be discarded.

Change-Id: I535467ec35fe2ae738ecae0a4f20d19ff4f001ec
Closes-Bug: #1250765
Merge "Debug env for tox"