Update unit test for synced folders

[legal90]

It's related to the new class for macvm guests: #448

[legal90]

Passes as expected:

Pending: (Failures listed here are expected and do not affect your suite's status)

  1) VagrantPlugins::Parallels::SyncedFolderMacVM prepare should share the folders
     # Not yet implemented
     # ./test/unit/synced_folder_macvm_test.rb:41

  2) VagrantPlugins::Parallels::SyncedFolder prepare should share the folders
     # Not yet implemented
     # ./test/unit/synced_folder_test.rb:51


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91 examples, 0 failures, 2 pending