sap_ha_install_hana_hsr: fixes to work for multiple secondaries

[ja9fuchs]

• improved some loops over the cluster nodes list using selectattr
• new task to validate that exactly 1 primary is defined and at least 1 secondary
• throttle 'secondary' tasks that execute on the primary at the same time otherwise and lead to conflicts
• some tasks only need to run once

This enables the base setup of Multi-Target System Replication.

Tested with 1 primary and 2 secondaries:

 sap_ha_install_hana_hsr_cluster_nodes:
      - hana_site: DC1
        node_name: su1hana1
        node_ip: <private node ip>
        node_role: primary
      - hana_site: DC2
        node_name: su1hana2
        node_ip: <private node ip>
        node_role: secondary
      - hana_site: DC3
        node_name: su1hana3
        node_ip: <private node ip>
        node_role: secondary

[marcelmamula]

LGTM, Tested on my cluster in AWS.