(maint) generate_rbac_token return token early

[Iristyle]

• If the rbac_token has already been generated, return its cached value rather than generating a new token.

  Provide the ability to force create a new one if necessary

  This allows test suites to properly setup a token before making a call to wait_for_pxp_agent_to_connect for instance

[Iristyle]

Pending a passing run at https://github.com/puppetlabs/pe-client-tools-vanagon/pull/313