fixes tcp and udp on the same port number GH-1108, GH-1109

fix a bug in forward_port_definitions() in Action::ForwardPorts
Lots more logging in with_target_vms
Only allow one provider active machine at a time.

Temporary limitation of Vagrant to only allow one active machine with a
provider at a time. That means you cant `up` a machine with both vmware
and virtualbox at the same time. In the future you will be able to but
to avoid various edge cases for now we're disallowing it.
Better test coverage on with_target_vms. Added pending tests to work on.
Environment#primary_machine_name and use it for with_target_vms

This makes the single-provider and default provider semantics work with
primary VMs.
active_machines should return name as a symbol
Convert provider to symbol
Convert provider to symbol only if non-nil
Fix some failing tests for 1.8.7.
One more final fix for 1.8.7
Fix guest plugin for RH & SUSE
DOC: keys/README.md -- fix urls to docs.
Merge pull request #1293 from yarikoptic/master

DOC: keys/README.md -- fix urls to docs.
Merge pull request #1260 from hdorio/master

Attempt to fix #1108, #1109, tcp and udp port on the same port number
Remove old `forward_port` method for configuration. Use `network`
Booting new VirtualBox VM should check for port collisions
Explicitly set error handling for port collision on resume
Remove network validation on config. We'll re-add this later.
VirtualBox forwarding port uses new `network` calls
Temporarily disable Network action while it is broken