CLI system tests may fail if output exceeds 1 MB

[t1m0thyj]

The runCliScript method in the TestUtils module calls child_process.spawnSync which has a default maxBuffer value of 1 MB (see Node.js doc).

Some CLI system tests, particularly ones for the zowe logs list logs command added in #1146, may write >1MB to stdout. When this happens, response.status is null and response.signal is SIGTERM, causing system tests that expect response.status == 0 to fail.

To resolve this, we could increase maxBuffer for all system tests, or at least for ones where we know a larger buffer size may be needed. Alternatively, we could allow for response.status == null in system tests, but that seems undesirable.