ci: fix test script to recognize any non-zero exit as an error

hack/linter.sh didn't properly install golangci-lint in hack/bin as I
already have another version of golangci-lint on my PATH, but then it
failed to execute because it was looking for it specifically in
hack/bin.

When the executable is not found, the exit code is 127 instead of 1,
and so test.sh ignored the error.

Two fixes:

1. `test.sh`:
  - Use `if (script) ...` instead of assigning / checking a result
    variable to determine if each validation script passed or failed.

2. `hack/linter.sh`:
  - Instead of checking for golangci-lint on the path, just
    specifically check for an executable file (`test -x`) in the
    expected location.

hack/linter.sh

@@ -16,12 +16,12 @@
 
 set -e -o pipefail
 
-DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 BIN=${DIR}/bin
 
-if ! [ -x "$(command -v golangci-lint)" ]; then
+if [ ! -x "${BIN}/golangci-lint" ]; then
 	echo "Installing GolangCI-Lint"
-	${DIR}/install_golint.sh -b ${BIN} v1.23.7
+	"${DIR}/install_golint.sh" -b "${BIN}" v1.23.7
 fi
 
-${BIN}/golangci-lint run
+"${BIN}/golangci-lint" run

scripts/test.sh

@@ -37,15 +37,11 @@ fail=0
 for s in "${scripts[@]}"
 do
     echo "RUN ${s}"
-    set +e
-    ./$s
-    result=$?
-    set -e
-    if [[ $result  -eq 1 ]]; then
+    if "./${s}"; then
+        echo -e "${GREEN}PASSED${RESET} ${s}"
+    else
         echo -e "${RED}FAILED${RESET} ${s}"
         fail=1
-    else
-        echo -e "${GREEN}PASSED${RESET} ${s}"
     fi
 done
 exit $fail