vcl: fix vcl_test.py sonarcloud issue

- Updated comment to indicate the original
  intermittent test failure still occurs when
  running make test with TEST_JOBS > 1.
- The original workaround has been retained
  until the root cause can be determined to
  avoid test failures in the LF CI infra
  with patches containing non-vcl code changes.

Type: test

Signed-off-by: Dave Wallace <dwallacelf@gmail.com>
Change-Id: I2645acd4bf2b16fbb2b0e297c8c2919fc6199c13