Use packages.zerovm.org instead of zvm.rackspace.com

It is only the first package that actually exist in the new domain,
the libzmq3-dev_4.0.1-ubuntu1_amd64.deb package seems to be gone.
We'll have to sort this out later.
Merge pull request #7 from mgeisler/master

Use packages.zerovm.org instead of zvm.rackspace.com