Abstract the request id logic in a module

[#53895047]
Remove unused EM-only code in ServiceGatewayClient

The EM-only code did not send necessary headers (the auth token), so it
would not have worked. We assume from this that it is unused in
production
[#53895047]
Extract http communication into separate class

Also improve testing
[#53895047]
Send the current request id in gateway calls

[#53895047]
Revert "Class to configure/send exceptions to a "Squash" notification service"

This reverts commit 7dadf0b597512a6def7694ee9c6449b9b9516315.

Conflicts:
	lib/cf/exception_notifier.rb
	vcap_common.gemspec
Don't raise exception when request id is unset

[#53895047]
HttpClient requires request_id

Also remove VCAP::Request

[#53895047]
Add new fields to ServiceErrorResponse
Remove GatewayExternalError

This exception was never handled any differently than a standard
ErrorResponse.

[#55121498]
Ensure service errors include new fields
Move service error info to an error hash
Support for ssl service gateways.