show return code when sending L1CTL_FBSB_REQ fails

Provide a little bit more information when a BTS test fails
due to L1CTL FBSB failure.

Example output:
Test case TC_si_sched_default finished. Verdict: fail reason: \
  FBSB Failed with non-zero return code 255

Change-Id: I5e8f23a2615b64bdf3167d486ba808c93f0f4b23
1 file changed