Use role in insensitive case in keystoneauth.

Using insensitive case could tolerate human error. For example,
user maybe set like this "operator_roles = Admin, swiftoperator"

- also fix a mistake in test, ['admin'] is correct value for roles, not
  'admin' (it will be looped as ['a', 'd', 'm', 'i', 'n'])
- add test for insensitive cases

Fixes: bug #1013120
Change-Id: I56d71da8bc503e48e92dd743692ba6fc237f029e