tmt reportportal plugin not reporting multi-host test results properly

[kkaarreell]

When importing test results from a multi-host test to RP, just a single (the first) test case instance is reported, despite the fact that the same test was running also on other guests.

[happz]

The same happens to tests with custom results. Such a test may easily produce more than one result per invocation, and once again, only the first one is reported to RP.

Generally, there can be more results of a given test & serial number pair, some may differ in their guest property, and some may even have a name different from that of the test.

[kkaarreell]

This is being worked on in https://github.com/teemtee/tmt/pull/3135