bbstagein: log entries for different jobs being merged or truncated

[adammoody]

Describe the bug
On a system with multiple BB jobs running at once, we are seeing log entries in bbstagein that are being merged and/or truncated. For example below you can see the "arg[0] = 1" for job 241866 is written starting in the middle of a json string from job 241812:

Job 241812: rc = 0
Job 241812: Changing mode for mount point /mnt/bb_2c3c6bd8038b4787e81527471bd8e6c6
Job 241812:
Job 241812: cmd: /opt/ibm//bb/bin/bbcmd --jobstepid=1 --target=0- --bcast chmod --path=/mnt/bb_2c3c6bd8038b4787e81527471bd8e6c6 --mode=0750
Job 241812: json: {"id":"1","rc":"0","0":{"id":"1","rc":"0","in":{"apicall":"BB_ChangeMode","parms":{"path":"\/mnt\/bb_2c3c6bd8038b4787e81527471bd8e6c6","newmode":"750"},"misc":{"uid":"0","gid":"0"}},"env":{"jobid":"241812","jobstepid":"1","contribid":"0"}},"1":{"id":"1","rc":"0","in":{"apicall":"BB_ChangeMode","parms":{"path":"\/mnt\/bb_2c3c6bd8038Job 241866: argv[0] = 1
Job 241866: HOSTLIST: lassen112,lassen440,lassen454,lassen111

It's not clear whether information is lost or just listed later into the log file.

To Reproduce

Expected behavior
This makes it hard to read the logs. We're hoping a fix can be added to keep the lines separate.

Screenshots
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Environment (please complete the following information):

• Machine [e.g. c123f01p01, WSC, national labs]
• Version [e.g. CSM 1.2.0]

ibm-burstbuffer-1.5.3-2161.ppc64le
ibm-burstbuffer-tools-1.5.3-2161.ppc64le
ibm-burstbuffer-lsf-1.5.3-2161.ppc64le
ibm-burstbuffer-tests-1.5.3-2161.ppc64le
ibm-burstbuffer-mn-1.5.3-2161.ppc64le

Additional context
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Issue Source:
Reasoning for opening this issue; a description of why this issue was opened; a link to another thread that spawned the need for opening this issue.