Build: Introduce shellcheck (#18081)

* Build: introduce shellcheck

Fixes #16198

scripts/circle-test-postgres.sh

@@ -1,17 +1,10 @@
 #!/bin/bash
-function exit_if_fail {
-    command=$@
-    echo "Executing '$command'"
-    eval $command
-    rc=$?
-    if [ $rc -ne 0 ]; then
-        echo "'$command' returned $rc."
-        exit $rc
-    fi
-}
+
+# shellcheck source=./scripts/helpers/exit-if-fail.sh
+source "$(dirname "$0")/helpers/exit-if-fail.sh"
 
 export GRAFANA_TEST_DB=postgres
 
 time for d in $(go list ./pkg/...); do
- exit_if_fail go test -tags=integration $d
-done
+ exit_if_fail go test -tags=integration "$d"
+done