Add tests get_hpos_app_health result

[JettTech]

Reason for Update:
Doubts surfaced about how the get_hpos_app_health call would respond if an error occurs with the conductor admin interface as well as how to distinguish between no hpos apps installed and a failed call. The expected behavior is for the value to return an option of None whenever the call fails and Some(<hpos_app_list>) whenever the call succeeds - with an empty hashmap for the value of hpos_app_list as the indicator of no installed happs on the hpos.

Tests Added:

• Test for ws creation and list_apps call to admin interface
• Test for a None value for hpos_app_list whenever a ws connection fails
• Test for a Some value for hpos_app_list whenever a ws connection succeeds

To Test:
cargo run test

[peeech]

Code looks great, just one thing that README needs updating.