add example error plugin

Make a plugin which always errors to test failure paths.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

examples/error-plugin.rs

@@ -0,0 +1,40 @@
+//! This is just an example plugin, do not use it in production!
+
+use netavark::{
+    network::types,
+    new_error,
+    plugin::{Info, Plugin, PluginExec, API_VERSION},
+};
+
+fn main() {
+    let info = Info::new("0.1.0-dev".to_owned(), API_VERSION.to_owned(), None);
+
+    PluginExec::new(Exec {}, info).exec();
+}
+
+struct Exec {}
+
+impl Plugin for Exec {
+    fn create(
+        &self,
+        _network: types::Network,
+    ) -> Result<types::Network, Box<dyn std::error::Error>> {
+        Err(new_error!("create error"))
+    }
+
+    fn setup(
+        &self,
+        _netns: String,
+        _opts: types::NetworkPluginExec,
+    ) -> Result<types::StatusBlock, Box<dyn std::error::Error>> {
+        Err(new_error!("setup error"))
+    }
+
+    fn teardown(
+        &self,
+        _netns: String,
+        _opts: types::NetworkPluginExec,
+    ) -> Result<(), Box<dyn std::error::Error>> {
+        Err(new_error!("teardown error"))
+    }
+}