Bug: adding an IdP and a new Saml RP do not combine in the journey

[mrochon]

Adding SAML RP wdoes not know about all the custom IdPs added below the Base.xml. The resulting SAML_SUSI journey therefore does not include these IdPs. Adding IdPs after adding SAML has a bug which causes it not to add CombinedSignupSignIn steps to an existing journey in an RP xml. Repro:

1. Add-IefPoliciesIdP - susi/edit updated correctly to use the idP
2. new-IefPoliciesSamlRP - new SAML_SUSI does not include the new IdPs
   Doing in reverse sequence does not help. Need to implement a more generic xml merge functionality.