Make default log alert conditional

Allow using the default `log` alert for both up and down alerts using
Go's templating conditionals. Following this example can do away with
the need for an up and down version of every alert.

README.md

@@ -93,6 +93,7 @@ Also, when alerts are executed, they will be passed through Go's format function
 |`{{.LastCheckOutput}}`|The last returned value from the check command to either stderr or stdout|
 |`{{.LastSuccess}}`|The ISO datetime of the last successful check|
 |`{{.MonitorName}}`|The name of the monitor that failed and triggered the alert|
+|`{{.IsUp}}`|Indicates if the monitor that is alerting is up or not. Can be used in a conditional message template|
 
 ### Metrics
 

alert.go

@@ -124,7 +124,7 @@ func NewLogAlert() *Alert {
 		Command: CommandOrShell{
 			Command: []string{
 				"echo",
-				"{{.MonitorName}} check has failed {{.FailureCount}} times",
+				"{{.MonitorName}} {{if .IsUp}}has recovered{{else}}check has failed {{.FailureCount}} times{{end}}",
 			},
 		},
 	}

alert_test.go

@@ -76,6 +76,24 @@ func TestAlertSend(t *testing.T) {
 			"Command shell with legacy template",
 			true,
 		},
+		// Test default log alert down
+		{
+			*NewLogAlert(),
+			AlertNotice{MonitorName: "Test", FailureCount: 1, IsUp: false},
+			"Test check has failed 1 times\n",
+			false,
+			"Default log alert down",
+			false,
+		},
+		// Test default log alert up
+		{
+			*NewLogAlert(),
+			AlertNotice{MonitorName: "Test", IsUp: true},
+			"Test has recovered\n",
+			false,
+			"Default log alert up",
+			false,
+		},
 	}
 
 	for _, c := range cases {