build: Address issues found by 1.43.0 clippy

These are mostly due to use of "bare use" statements and unnecessary vector
creation.

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

vhost_user_block/src/lib.rs

@@ -13,7 +13,6 @@ extern crate vhost_rs;
 extern crate vhost_user_backend;
 extern crate vm_virtio;
 
-use epoll;
 use libc::EFD_NONBLOCK;
 use log::*;
 use qcow::{self, ImageType, QcowFile};