KnoxSSO Token Expiration should be Optional

The KnoxSSO service needs to be able to configure a token to have no expiration time. This will allow the lifecycle of the token within the SSO cookie to be the same as the cookie itself.

By indicating a -1 as the knoxsso.token.ttl parameter value within the KnoxSSO service descriptor in the topology, the lifecycle will be in lock step with the cookie itself.