elbadmin dies if terminated, non-extant instances are present in an ELB

43c9d71ab241a47cd8a5d2caebc368fcbeff7b65 added printing of the ```Name``` tag for instances in an ELB.  7de7ca16a5e672bdf5251eb7204caa0bf9a39e2c changed that new feature to only pull ```Name``` tags for instances in the ELB.  However, terminated instances can remain in an ELB.  Terminated instances can be queried for a time, but querying them eventually returns a 400 error of ```Client.InvalidInstanceID.NotFound```.

This patch reverts to enumerating all instances, but only requests the Name tag for extant instances.  This is likely more reliable than, say, relying on the ```Instance is in terminated state.``` message.

```elbadmin``` has no tests, so no test is added for this change.