Add proxy to apt class
Add proxy to apt class

This commit adds a proxy to the apt class in the
pre config manifest.

This is because I am using a squid proxy to speed
up testing in my environment.

I need to expose this as a config option so that
the hardcoded address of my app proxy is not
required for anyone to use this.

huntxu/fuel-library,Metaswitch/fuel-library,xarses/fuel-library,eayunstack/fuel-library,huntxu/fuel-library,Metaswitch/fuel-library,slystopad/fuel-lib,huntxu/fuel-library,ddepaoli3/fuel-library-dev,eayunstack/fuel-library,SmartInfrastructures/fuel-library-dev,ddepaoli3/fuel-library-dev,zhaochao/fuel-library,Metaswitch/fuel-library,zhaochao/fuel-library,Metaswitch/fuel-library,xarses/fuel-library,ddepaoli3/fuel-library-dev,eayunstack/fuel-library,stackforge/fuel-library,eayunstack/fuel-library,SmartInfrastructures/fuel-library-dev,slystopad/fuel-lib,xarses/fuel-library,zhaochao/fuel-library,stackforge/fuel-library,huntxu/fuel-library,slystopad/fuel-lib,stackforge/fuel-library,ddepaoli3/fuel-library-dev,eayunstack/fuel-library,zhaochao/fuel-library,huntxu/fuel-library,xarses/fuel-library,SmartInfrastructures/fuel-library-dev,SmartInfrastructures/fuel-library-dev,SmartInfrastructures/fuel-library-dev,stackforge/fuel-library,slystopad/fuel-lib,ddepaoli3/fuel-library-dev,zhaochao/fuel-library