crosvm: add a feature to disable sandbox by default

Add a build-time feature that allows having plugin and other parts of
crosvm to run outside of jailed environment. This is strictly a
development time feature and is not expected to be activated with
shipping code.

Sandbox can still be activated by passing -u (--multiprocess) option.

BUG=None
TEST=cargo test --feature=default-no-sandbox

Change-Id: If9ef1ce8ed0b5d23cef3ad193679baca94413360
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1054194
Reviewed-by: Zach Reizner <zachr@chromium.org>

Cargo.toml

@@ -11,6 +11,7 @@ panic = 'abort'
 
 [features]
 plugin = ["plugin_proto", "crosvm_plugin", "protobuf"]
+default-no-sandbox = []
 
 [dependencies]
 arch = { path = "arch" }

src/main.rs

@@ -92,7 +92,7 @@ impl Default for Config {
             vhost_net: false,
             wayland_socket_path: None,
             socket_path: None,
-            multiprocess: true,
+            multiprocess: !cfg!(feature = "default-no-sandbox"),
             seccomp_policy_dir: PathBuf::from(SECCOMP_POLICY_DIR),
             cid: None,
             plugin: None,