Locked gitian-builder to working commit
Removed nl_NL.UTF-8 from locale.gen
Do not overwrite already existing downloaded input sources
Use COPY in place of ADD in Dockerfile's
* avoid chown long time operation by chown'ing specific files
* use correct list filenames
* removed libpng (not used for Linux builds)
* use docker kill instead of stop
* removed extra environment cleanup from bash_profile and added proper gitian-builder patch
* use gitian-host-vms for gitian-bitcoin-host
* fixed issue at stopping container after generation of base VMs
