Add proxy support

@brettweavnet-intuit @grantleehoffman @keviny22 @vsomayaji 

I modified the AWS codedeploy plugin to utilize a proxy server.  This version of the codedeploy plugin now works behind our proxy server in QDC on our internal Jenkins system.  

I tried using the global settings noted here https://wiki.jenkins-ci.org/display/JENKINS/JenkinsBehindProxy
but those did not work (as I suspected).  The client connection object needed to be told about the proxy upon creation.  These changes reflect the required updates and have been tested and appear to work.

I would like to get another pair of eyes before I submit a pull request back to AWS.

HERE IS THE TIMEOUT ERROR WITHOUT THESE CHANGES:
Nov 24, 2014 11:50:41 PM com.amazonaws.http.AmazonHttpClient executeHelper
INFO: Unable to execute HTTP request: Connect to codedeploy.us-west-2.amazonaws.com:443 timed out
org.apache.http.conn.ConnectTimeoutException: Connect to codedeploy.us-west-2.amazonaws.com:443 timed out
	at org.apache.http.conn.ssl.SSLSocketFactory.connectSocket(SSLSocketFactory.java:416)
	at com.amazonaws.http.conn.ssl.SdkTLSSocketFactory.connectSocket(SdkTLSSocketFactory.java:112)
	at