[6.15.z] Refactor and simplify ping test

[Satellite-QE]

Cherrypick of PR: #13489

Cache status was added to hammer ping output and there can be more cache servers configured so the output syntax has changed. I changed and simplified the test so it can parse current output and it also meets test description.

sample output:

database:         
    Status:          ok
    Server Response: Duration: 0ms
cache:            
    servers: 
     1) Status:          ok
        Server Response: Duration: 0ms
candlepin:        
    Status:          ok
    Server Response: Duration: 23ms
...

PS: I'm not aware of negative scenario for this testcase (i.e. scenario when some of Satellite services report status "FAIL"). We may add it in future.

[Satellite-QE]

trigger: test-robottelo
pytest: tests/foreman/cli/test_ping.py

[ogajduse]

PRT passed