wait_for_instances optional param in run_instances

##### Optional parameter in boto.ec2.connection.run_instances()

Encapsulates the waiting until all the instances are in running state. The function will return the reservation object as soon all instances are ready.


##### example
```
#!/usr/bin/env python

import boto

ec2 = boto.connect_ec2()
res = ec2.run_instances("ami-018c9568", instance_type="t1.micro", 
                        min_count=10, max_count=10, wait_for_instances=True)
print 'ready!'

for instance in res.instances:
    print instance.ip_address
```