Add end-to-end Test

- Add an infrastructur to run local e2e tests.
- Add some tests.

docker/mta_provision/usr/bin/prepare.sh

@@ -7,8 +7,8 @@ echo "127.0.0.1 " $(hostname) > /etc/hosts
 echo "127.0.0.2 example.com" >> /etc/hosts
 
 ## build milter
-if [ -f /opt/husk/mapped/husk ] ; then
-  HUSK_BIN=/opt/husk/mapped/husk
+if [ -f /opt/husk/mapped/Cargo.toml ] ; then
+  HUSK_BIN=/opt/husk/mapped/target/release/husk
 else 
   cd /opt/husk
   git clone https://gitlab.com/husk-project/husk-milter.git