formatting and logging improvements to bosh_aws_cpi instance manager

Signed-off-by: Dmitriy Kalinin <dmitriy@pivotallabs.com>
use instance_double in bosh_aws_cpi instance manager

Signed-off-by: Dmitriy Kalinin <dmitriy@pivotallabs.com>
extracted Instance class in bosh_aws_cpi

Signed-off-by: Karl Isenberg <kisenberg@pivotallabs.com>
terminate instances that were not successfully configured by the aws cpi

cerate_vm cpi method should do its best to either successfully return instance id or raise an error and clean up created resources