mgr/ansible: Host ls implementation

mgr/ansible: Host ls implementation

Implement the <<host ls>> operation in the orchestrator

Example:
[ ~]$ ceph orchestrator host ls
Hosts
192.168.121.20
192.168.121.170
192.168.121.213
192.168.121.212

Followed @sebastian-philipp suggestions
- Improved exception management in process_hosts_ls
- use the orchestrator <get_host> function instead <host_ls>
- Orchestrator now returns a list of Inventory Node
- Orchestrator-cli use the list of inventory nodes to print the hosts names
- Fixed comparation error
- <process_hosts_ls> method: include json errors in output
- removed <host_ls> orchestrator method stuff (<get_hosts> is the new method to use)
- Fixed wrong assignations
- rebased
02/01/19:
- Addressed @sebastian-philipp suggestions
- Housekeeping tasks.
- Refactor completion's result management. Created Output wizards and basic unit tests for them.
- rebased

Signed-off-by: Juan Miguel Olmo Martínez <jolmomar@redhat.com>