update shell scripts according to shellcheck recommendations and minor cleanup

util/run-gnu-test.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 # spell-checker:ignore (env/vars) BUILDDIR GNULIB SUBDIRS
-cd "$(dirname "${BASH_SOURCE[0]}")/../.."
+cd "$(dirname -- "$(readlink -fm -- "$0")")/../.."
 set -e
 BUILDDIR="${PWD}/uutils/target/release"
 GNULIB_DIR="${PWD}/gnulib"
@@ -13,4 +13,5 @@ if test -n "$1"; then
     export RUN_TEST="TESTS=$1"
 fi
 
+#shellcheck disable=SC2086
 timeout -sKILL 2h make -j "$(nproc)" check $RUN_TEST SUBDIRS=. RUN_EXPENSIVE_TESTS=yes RUN_VERY_EXPENSIVE_TESTS=yes VERBOSE=no || : # Kill after 4 hours in case something gets stuck in make