vmm: http: Convert to micro_http HttpServer

The new micro_http package provides a built-in HttpServer wrapper for
running a more robust HTTP server based on the package HTTP API.

Switching to this implementation allows us to, among other things,
handle HTTP requests that are larger than 1024 bytes.

Fixes: #423

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

vmm/Cargo.toml

@@ -33,7 +33,6 @@ vm-allocator = { path = "../vm-allocator" }
 vm-virtio = { path = "../vm-virtio" }
 vmm-sys-util = ">=0.1.1"
 signal-hook = "0.1.10"
-threadpool = "1.0"
 
 [dependencies.linux-loader]
 git = "https://github.com/rust-vmm/linux-loader"