swarm/dev: add development environment (#14332)

This PR adds a Swarm development environment which can be run in a
Docker container and provides scripts for building binaries and running
Swarm clusters.

swarm/dev/scripts/util.sh

@@ -0,0 +1,53 @@
+# shared shell functions
+
+info() {
+  local msg="$@"
+  local timestamp="$(date +%H:%M:%S)"
+  say "===> ${timestamp} ${msg}" "green"
+}
+
+warn() {
+  local msg="$@"
+  local timestamp=$(date +%H:%M:%S)
+  say "===> ${timestamp} WARN: ${msg}" "yellow" >&2
+}
+
+fail() {
+  local msg="$@"
+  say "ERROR: ${msg}" "red" >&2
+  exit 1
+}
+
+# say prints the given message to STDOUT, using the optional color if
+# STDOUT is a terminal.
+#
+# usage:
+#
+#   say "foo"              - prints "foo"
+#   say "bar" "red"        - prints "bar" in red
+#   say "baz" "green"      - prints "baz" in green
+#   say "qux" "red" | tee  - prints "qux" with no colour
+#
+say() {
+  local msg=$1
+  local color=$2
+
+  if [[ -n "${color}" ]] && [[ -t 1 ]]; then
+    case "${color}" in
+      red)
+        echo -e "\033[1;31m${msg}\033[0m"
+        ;;
+      green)
+        echo -e "\033[1;32m${msg}\033[0m"
+        ;;
+      yellow)
+        echo -e "\033[1;33m${msg}\033[0m"
+        ;;
+      *)
+        echo "${msg}"
+        ;;
+    esac
+  else
+    echo "${msg}"
+  fi
+}