[SCT] Reconfigure some tests to use hostname instead of ip addresses while adding the cluster

[mikliapko]

It was suggested to extend test coverage for Manager SCT tests to use hostnames in --host key of sctool add cluster command.

What to do:

• Investigate on whether we do something like that in some dtests or dev integration tests. If yes, then it may possibly eliminate the need to it in SCT as well.
• If not, change the test configuration to use hostnames for some of the Manager tests.

[mikliapko]

Added refinement-needed label to discuss an importance of such a change with dev team