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>

Cargo.toml

@@ -65,4 +65,5 @@ members = [
     "arch_gen",
     "net_gen",
     "vm-allocator",
+    "option_parser"
 ]