Build: Introduce shellcheck (#18081)

* Build: introduce shellcheck

Fixes #16198

scripts/circle-test-backend.sh

@@ -1,14 +1,7 @@
 #!/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"
 
 echo "building backend with install to cache pkgs"
 exit_if_fail time go install ./pkg/cmd/grafana-server
@@ -16,5 +9,5 @@ exit_if_fail time go install ./pkg/cmd/grafana-server
 echo "running go test"
 set -e
 time for d in $(go list ./pkg/...); do
-  exit_if_fail go test -tags=integration -covermode=atomic $d
+  exit_if_fail go test -tags=integration -covermode=atomic "$d"
 done