Support for additional AWS configuration properties

Allow the following AWS configuration properties to be propagated from the MicroBOSH deployment
manifest to the AWS SDK:
- ec2_endpoint
- elb_endpoint
- max_retires
- http_read_timeout
- http_wire_trace
Do not have to check for values as they are alway there from default values

Signed-off-by: Phan Le <ple@pivotal.io>