Failed to create private network: virtual network named vagrant-vnet already exists

[legal90]

If virtual network vagrant-vnet0 already exists (say, you've created yet another private network before), Vagrant will fail to create the new one:

...
==> default: Setting the default configuration for VM...
==> default: Setting the name of the VM: work_default_1452697089803_93251
==> default: Fixed port collision for 22 => 2222. Now on port 2200.

stderr: There was an error while command execution. The command and stderr is shown below.

Command: ["/usr/local/bin/prlsrvctl", "net", "add", "vagrant-vnet", "--type", "host-only"]

Stderr: Failed to add Virtual Network vagrant-vnet: A virtual network named vagrant-vnet already exists. Specify another name for this virtual network.

This is a regression introduced by 827dfdf in vagrant-parallels v1.6.0