Replaced usage of deprecated commons-httpclient with org.apache.httpcomponents.

Replaced the usage of the deprecated `org.springframework.http.client.CommonsClientHttpRequestFactory` with the current `org.springframework.http.client.HttpComponentsClientHttpRequestFactory` when creating the HTTP client for `RestTemplate`. This makes cloudfoundry-client-lib compatible with Spring 4.x. 

Patch courtesy of @mstine.