Roll forward of 3904ac3 (3904ac3). Fix #4625 by running the test proc…

…ess in a sub-shell.

Apparently, nested background processes interfere with SIGINT handling in bash. I don't 100% understand why and how, but I do have a small bash script that demonstrates the problem: script A that spawns a background process, sends it a SIGINT, and verifies it was received. The script works, *unless* run in the background by a process B; this extra layer of backgrounding cause process A's logic to stop working. See experimental/users/olaola/shell/ for examples. See also https://stackoverflow.com/questions/48847722/nested-background-processes-and-sigint-handling

*** Original change description ***

Fixing test-setup.sh occasionally missing stdout/stderr, on systems where "tail --pid" is supported.

The solutions aren't mine, the new test was taken from Ola's unknown commit and the way to avoid race condition courtesy of sethkoehler@

Mitigates #4608 for compatible Linux systems.

TESTED=presubmits, manual shell tests on new bazel
RELNOTES: None
PiperOrigin-RevId: 186312008

tools/test/test-setup.sh

@@ -227,10 +227,10 @@ tail -fq --pid $pid -s 0.001 /dev/null &> /dev/null || has_tail=false
 if [ "$has_tail" == true ] && [  -z "$no_echo" ]; then
   touch "${XML_OUTPUT_FILE}.log"
   if [ -z "$COVERAGE_DIR" ]; then
-    "${TEST_PATH}" "$@" &>"${XML_OUTPUT_FILE}.log" &
+    ("${TEST_PATH}" "$@" &>"${XML_OUTPUT_FILE}.log") &
     pid=$!
   else
-    "$1" "$TEST_PATH" "${@:3}" &> "${XML_OUTPUT_FILE}.log" &
+    ("$1" "$TEST_PATH" "${@:3}" &> "${XML_OUTPUT_FILE}.log") &
     pid=$!
   fi
   tail -fq --pid $pid -s 0.001 "${XML_OUTPUT_FILE}.log"