ci: Fix error-masking bug and improve debugability in L0_trace

[rmccorm4]

Changes:

• Remove invalid check for trace_mode after expected error that always produced RET=1 because the curl.out only contained {"error": ...} but we checked for trace_mode count to be non-zero
• Remove RET=0 reset in middle of script - this was masking the error above
• Add 'cat curl.out' to various places that check the contents and may fail for easier visibility to error in logs. I had to repro the first 2 bullets locally to understand what was happening, so adding this to dump out the curl responses so we can better determine what

[oandreeva-nv]

lgtm, conditional on ci

[rmccorm4]

Job passed ✅