vmm: support setting cpu affinity with host cpu indices >255

On hosts with >256 cpus, setting the cpu affinity to a host cpu index
>255 will return an error because type of `host_cpu` is `u8`.
This commit changes the type of `host_cpu` to `usize` to remove this
limitation.

Signed-off-by: Sean Banko <sbanko@crusoeenergy.com>

vmm/src/config.rs

@@ -590,7 +590,7 @@ impl CpusConfig {
             .map_err(Error::ParseCpus)?
             .unwrap_or(DEFAULT_MAX_PHYS_BITS);
         let affinity = parser
-            .convert::<Tuple<u8, Vec<u8>>>("affinity")
+            .convert::<Tuple<u8, Vec<usize>>>("affinity")
             .map_err(Error::ParseCpus)?
             .map(|v| {
                 v.0.iter()