Make `cfy_manager add-networks` work in HA cluster

During the new `add-networks` command we:

1. Add the new network to the provider context

2. Add the new network to the /etc/cloudify/certificate_metadata file

3. Create new internal certificates

All managers in a cluster have to have to same certificates, but we currently don't sync certificates between them.
We need to make sure the new certificates are updated throughout the cluster, and to test that the new `add-networks` command actually work in a HA scenario.