* bhyve_command.c (bhyveBuildNetArgStr, virBhyveProcessBuildBhyveCmd):
  add dryRun mode which doesn't create any devices when enabled
* bhyve_command.c (virBhyveProcessBuildBhyveCmd,
  virBhyveProcessBuildDestroyCmd, virBhyveProcessBuildLoadCmd): accept
  virDomainDefPtr instead of virDomainObjPtr.

As we can use virBhyveCapsBuild() now, replace
testBhyveBuildCapabilities() with it.

At this point unittest covers 4 basic cases:

 - minimal working XML for bhyve
 - same as above, but with virtio disk
 - ACPI and APIC args test
 - MAC address test