[Rocm][CI] Enable 2-node test

[charlifu]

This PR tries to enable 2 node test by updating the command to use run-multi-node-test.sh when the step.num_nodes >= 2.

[Alexei-V-Ivanov-AMD]

I'm looking at the test group definition and it looks like a mixture of commands that should be run "bare-metal" (i.e. through the run-multi-node-test.sh, which spawns the provided container image for each of the two nodes) and things, like pytest invocations that are supposed to be running inside a single container (i.e. our standard testing path we do for all other tests).

Both single-image pytests are succeeding in my local run, as well as two first 2-node tests, however, the third is failing for me locally.

We need to change this PR to enable correct execution of the "2 Node Tests (4 GPUs in total) " test group.