Add ec2 gahp command EC2_VM_SERVER_TYPE. #3755

This new gahp command issues a simple ec2 command and analyzes the
response to determine which of several implementations the server is.
The implementations detected are Amazon, OpenStack, Nimbus, and
Eucalyptus. If the response doesn't look like any of these, "Unknown" is
returned.
Have gridmanager use new ec2 gahp command EC2_VM_SERVER_TYPE. #3755

Track the server type of each resource the gridmanager talks to, and
save the server type in the ad of submitted jobs in the new attribute
EC2ServerType.
Further work using ssh keypair for OpenStack EC2 submission. #3682

Use auto-detection of ec2 server type to decide if we need to use the
ssh keypair for two-phase submission.
Improve cleanup of ssh keypairs.