Add Floaty self-test nagios check script

Add the script to the generated packages as
`/usr/lib/nagios/plugins/floaty-self-test`

.goreleaser.yml

@@ -43,6 +43,11 @@ nfpms:
       - deb
       - rpm
       - apk
+    contents:
+      - src: floaty-self-test.sh
+        dst: /usr/lib/nagios/plugins/floaty-self-test
+        file_info:
+          mode: 0755
 
 release:
   prerelease: auto

README.md

@@ -182,6 +182,10 @@ Keepalived.
 /bin/floaty --json-log --verbose --test /etc/floaty.yml
 ```
 
+The Debian, RPM and Alpine packages generated by `goreleaser` include script `floaty-self-test.sh` as `/usr/lib/nagios/plugins/floaty-self-test`.
+This script runs Floaty in test mode and expects a config file as its only argument.
+The script is intended to be used as a check script for an Icinga2 check.
+
 ### FIFO mode
 
 Floaty can run in FIFO mode allowing it to process notification events through a FIFO instead of using notify scrips 

floaty-self-test.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+set -u -o pipefail
+
+if [ $# -eq 0 ]; then
+  echo "Usage: $0 /path/to/floaty-config.yaml"
+  exit 3
+elif [ "$1" == "-h" ] || [ "$1" == "--help" ]; then
+  echo "Usage: $0 /path/to/floaty-config.yaml"
+  exit 3
+fi
+
+floaty_bin=/usr/bin/floaty
+config_file="$1"
+
+if [ ! -f "$config_file" ]; then
+  echo "Floaty config file doesn't exist: ${config_file}"
+  exit 3
+fi
+
+self_test_output=$("$floaty_bin" -T "$config_file" 2>&1)
+self_test_exit=$?
+
+if [ $self_test_exit -eq 0 ]; then
+  echo "Floaty self-test passed"
+  exit 0
+else
+  echo -e "Floaty self-test failed\n"
+  echo -e "${self_test_output}"
+  exit 2
+fi