vhost_user_net, vhost_user_block, option_parser: Remove vmm dependency

Remove the vmm dependency from vhost_user_block and vhost_user_net where
it was existing to use config::OptionParser. By moving the OptionParser
to its own crate at the top-level we can remove the very heavy
dependency that these vhost-user backends had.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vmm/src/lib.rs

@@ -6,6 +6,7 @@
 extern crate anyhow;
 extern crate arc_swap;
 extern crate hypervisor;
+extern crate option_parser;
 #[macro_use]
 extern crate lazy_static;
 #[macro_use]