ec2_launch: Simplify the logic for getting the IP address

Use the function waituntil() available in the integration-test branch
to simplify the code that retrieves the IP of the instance.

A 'TODO' note was also added to remember us to merge this function
once it gets merged.

bootstrapvz/plugins/ec2_launch/tasks.py

@@ -1,10 +1,20 @@
 from bootstrapvz.base import Task
 from bootstrapvz.common import phases
 from bootstrapvz.providers.ec2.tasks import ami
-import time
 import logging
 
 
+# TODO: Merge with the method available in wip-integration-tests branch
+def waituntil(predicate, timeout=5, interval=0.05):
+	import time
+	threshhold = time.time() + timeout
+	while time.time() < threshhold:
+		if predicate():
+			return True
+		time.sleep(interval)
+	return False
+
+
 class LaunchEC2Instance(Task):
     description = 'Launching EC2 instance'
     phase = phases.image_registration
@@ -40,27 +50,18 @@ class PrintPublicIPAddress(Task):
             filename = '/dev/null'
         f = open(filename, 'w')
 
-        i = 0
-        instance = None
-        while True:
-            logger.debug('Waiting a bit to get instance metadata...')
-            time.sleep(5)
-
-            i += 1
-            if i > 10:
-                logger.error('Waited too much, giving up')
-                break
-
         r = ec2['connection'].get_only_instances([ec2['instance_id']])
         if not r and not r[0]:
             logger.error('Could not get instance metadata')
-                break
-
+            f.write('')
+        else:
             instance = r[0]
-            if instance.ip_address:
-                break
 
-        if instance and instance.ip_address:
+            def instance_has_ip():
+                instance.update()
+                return instance.ip_address
+
+            if waituntil(instance_has_ip, timeout=120, interval=5):
                 logger.info('******* EC2 IP ADDRESS: %s *******' % instance.ip_address)
                 f.write(instance.ip_address)
             else: