EC2 VPC public DNS hostname support - EUCA-9826

VPC instances now respect the VPC hostnames enabled flag for public and
private DNS hostnames. Network interfaces are updated to include the
public and private DNS hostnames when appropriate.

EUCA-9826
EC2 VPC association events for EIPs / instances via ENIs - EUCA-9833

A new address state (started) is added to reflect when an address is in
use by a running instance. On instance run / start / stop / terminate
the address state is updated as appropriate in addition to the regular
address associate / disassociate actions.

EUCA-9833
Merge remote-tracking branch 'origin/dev/sjones/EUCA-9833' into testing