update IB_DEVICES specification logic to fix ib-loopback test regression

[henryli001]

Description

The ib-loopback test was regressed due to this recent change. When running ib-loopback using the standard config, the test would fail since it would pass numeric values like 0 into the test command which would break since it is not a valid IB device name.

Example failure:

 [2025-11-25 22:08:38,100 vmssnc6ec000003:141056][micro_base.py:200][INFO] Execute command - round: 0, benchmark: ib-loopback, command: /usr/local/bin/run_perftest_loopback 47 45 /usr/local/b                                                                                                                                                        in/ib_write_bw -s 8388608 -F --iters=20000 -d 0 -p 45617 -x 0 --report_gbits.
[0]: IB device 0 not found
 Unable to find the Infiniband/RoCE device
IB device 0 not found
 Unable to find the Infiniband/RoCE device
[2025-11-25 22:08:39,113 vmssnc6ec000003:141056][micro_base.py:209][ERROR] Microbenchmark execution failed - round: 0, benchmark: ib-loopback, error message: IB device 0 not found
 Unable to find the Infiniband/RoCE device
IB device 0 not found
 Unable to find the Infiniband/RoCE device

Major Revision

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Minor Revision

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