Bug 1998119

Description of problem:
Inappropriate error message "Couldn't connect to the server: undefined method `to_sym' for nil:NilClass" is shown when ping pulp3 fails during upgrade from 6.9.4 to 6.10(SNAP 14.0) due to https://bugzilla.redhat.com/show_bug.cgi?id=1996476

Version-Release number of selected component (if applicable):
6.10.0 SNAP14.0

How reproducible:
always

Steps to Reproduce:
1. Continue upgrade after content-switchover fails (as described in BZ#1996476) (maybe some other procedure that causes pulp3 to return 503?)
2. # satellite-maintain upgrade run --target-version 6.10 --whitelist "repositories-validate,repositories-setup,content-switchover"

Actual results:
Following error message is displayed
--------------------------------------------------------------------------------
Check whether all services are running using the ping call:           [FAIL]
Couldn't connect to the server: undefined method `to_sym' for nil:NilClass
--------------------------------------------------------------------------------

Expected results:
Error message should contain something like name of destination server or some different explanation, not "undefined method..."

Additional info:
# tail /var/log/foreman-maintain/foreman-maintain.log
...
D, [2021-08-25 15:58:57-0400 #77043] DEBUG -- : Called /katello/api/ping
D, [2021-08-25 15:58:57-0400 #77043] DEBUG -- : Response: 200,   {"status":"FAIL","services":{"candlepin":{"status":"ok","duration_ms":"43"},"candlepin_auth":{"status":"ok","duration_ms":"38"},"foreman_tasks":{"status":"ok","duration_ms":"3"},"katello_events":{"status":"ok","message":"0 Processed, 0 Failed","duration_ms":"0"},"candlepin_events":{"status":"ok","message":"0 Processed, 0 Failed","duration_ms":"0"},"pulp3":{"status":"FAIL","message":"503 Service Unavailable"},"pulp":{"status":"ok","duration_ms":"185"},"pulp_auth":{"status":"ok","duration_ms":"93"}}}
...

# hammer ping
...
pulp3:            
    Status:          FAIL
    Server Response: Message: 503 Service Unavailable
...