Make check scripts run pytest in parallel (quantumlib#5143)

The tests were made parallel in CI, but this updates the scripts to run in parallel. Respects if user overrides with different level of parallelism.

check/pytest

@@ -19,14 +19,22 @@ cd "$(git rev-parse --show-toplevel)"
 
 PYTEST_ARGS=()
 ACTUALLY_QUIET=""
+PARALLEL=""
 for arg in "$@"; do
     if [[ "${arg}" == "--actually-quiet" ]]; then
         ACTUALLY_QUIET=1
     else
+        if [[ "${arg}" == "-n" ]]; then
+            PARALLEL=1
+        fi
         PYTEST_ARGS+=("${arg}")
     fi
 done
 
+if [ -z "${PARALLEL}" ]; then
+    PYTEST_ARGS+=("-n=auto")
+fi
+
 source dev_tools/pypath
 PYTHON_VERSION=$(python -V 2>&1 | sed 's/.* \([0-9]\).\([0-9]\).*/\1\2/')
 if [ "$PYTHON_VERSION" -lt "37" ]; then

check/pytest-and-incremental-coverage

@@ -79,7 +79,7 @@ check/pytest --actually-quiet \
 pytest_result=$?
 
 
-# assume succesful cover_result in case coverage is not run
+# assume successful cover_result in case coverage is not run
 cover_result=0
 if (( $ANALYZE_COV )); then
     # Convert to .py,cover files.