Clean up ruby.

Swapped out instance_variable_set, which modifies internal object state directly, for send, which goes through public interfaces. Also broke the hash.inject call in keys_to_symbols out into multiple lines to make what's going on a bit clearer.

Testing revealed a bug in the vmware_fusion example's network block, which I hadn't updated for the latest Vagrantfile changes, so I fixed that while I was at it.