vars: Add trySlackSend function

Adds a new library function trySlackSend that echos the message to the
build log if the Slack Notification Plugin is not configured.

Signed-off-by: Geoff Levand <geoff@infradead.org>

vars/trySlackSend.groovy

@@ -0,0 +1,19 @@
+/*
+ * Sends a notification to Slack.  If the Slack Notification Plugin is not
+ * configured the the notification will be echoed to the Jenkins build log.
+ */
+
+def call(Map args) {
+    Map colorMap = [
+        'grey'    :'#C0C0C0',
+        'persian' :'#2020C0',
+    ]
+    String channel = args.channel ?: ''
+    String color = args.color ? colorMap.get(args.color, args.color) : 'good'
+
+    try {
+        slackSend(channel: channel, color: color, message: args.message)
+    } catch (NoSuchMethodError err) {
+        echo 'Slack Notification (' + args.color + '): ' + args.message
+    }
+}

vars/trySlackSend.txt

@@ -0,0 +1,6 @@
+The trySlackSend function sends a notification to Slack.  If the Slack
+Notification Plugin is not configured the the notification will be echoed to
+the Jenkins build log.
+
+Takes a string parameter 'message' and optional string parameters 'channel' and
+'color'.