Add option to disable network tests

`cargo xtask run` now takes a `--disable-network` arg that turns off the
network protocol tests by not creating a network device.

The purpose of this flag is to make the QEMU tests faster when iterating
on something locally. Disabling the network stuff drops the time down
from ~12.5s to ~4.5s. The extra time doesn't matter when running in CI,
but for quick local testing it can add up.

Author: nicholasbishop

xtask/src/opt.rs

@@ -101,6 +101,10 @@ pub struct QemuOpt {
     #[clap(long, action)]
     pub disable_kvm: bool,
 
+    /// Disable network tests.
+    #[clap(long, action)]
+    pub disable_network: bool,
+
     /// Disable some tests that don't work in the CI.
     #[clap(long, action)]
     pub ci: bool,

xtask/src/qemu.rs

@@ -523,7 +523,7 @@ pub fn run_qemu(arch: UefiArch, opt: &QemuOpt) -> Result<()> {
 
     // Attach network device with DHCP configured for PXE. Skip this for
     // examples since it slows down the boot some.
-    let echo_service = if opt.example.is_none() {
+    let echo_service = if !opt.disable_network && opt.example.is_none() {
         cmd.args([
             "-nic",
             "user,model=e1000,net=192.168.17.0/24,tftp=uefi-test-runner/tftp/,bootfile=fake-boot-file",