Add progress output while waiting for dependencies

This commit adds progress output while waiting for `depends_on`
conditions to resolve. The initial output looks like so:

     ⠿ Container chbench-zookeeper-1        Waiting      0s
     ⠿ Container chbench-kafka-1            Waiting      0s
     ⠿ Container chbench-one-off            Waiting      0s

Once all conditions have been resolved, the ouput looks like this:

     ⠿ Container chbench-zookeeper-1        Healthy      1.2s
     ⠿ Container chbench-kafka-1            Healthy      3.2s
     ⠿ Container chbench-schema-registry-1  Exited       4s

As shown above, `service_healthy` conditions result in a terminal status
of "Healthy" while `service_exited_successfully` conditions result in a
terminal status of "Exited".

Signed-off-by: Nikhil Benesch <nikhil.benesch@gmail.com>

pkg/progress/event.go

@@ -68,6 +68,21 @@ func StartedEvent(ID string) Event {
 	return NewEvent(ID, Done, "Started")
 }
 
+// Waiting creates a new waiting event
+func Waiting(ID string) Event {
+	return NewEvent(ID, Working, "Waiting")
+}
+
+// Healthy creates a new healthy event
+func Healthy(ID string) Event {
+	return NewEvent(ID, Done, "Healthy")
+}
+
+// Exited creates a new exited event
+func Exited(ID string) Event {
+	return NewEvent(ID, Done, "Exited")
+}
+
 // RestartingEvent creates a new Restarting in progress Event
 func RestartingEvent(ID string) Event {
 	return NewEvent(ID, Working, "Restarting")