help run mox with docker

in the Dockerfile, allow running on privileged ports and expose those ports.

add a docker-compose.yml with instructions for the quickstart.

fix running imaptest somewhat. after a short while it will hit the rate limiter.

in quickstart, recognize we are running under docker, and print slightly
different commands to set permissions, and skip generating the systemd service
file. als fix cleaning up the right paths during failure in quickstart.

for issue #3

docker-compose-imaptest.yml

@@ -1,7 +1,9 @@
 version: '3.7'
 services:
   mox:
-    build: .
+    build:
+      context: .
+      dockerfile: Dockerfile.moximaptest
     user: ${MOX_UID}:${MOX_GID}
     volumes:
       - ./testdata/imaptest/data:/mox/data
@@ -9,7 +11,8 @@ services:
       - ./testdata/imaptest/domains.conf:/mox/domains.conf
       - ./testdata/imaptest/imaptest.mbox:/mox/imaptest.mbox
     working_dir: /mox
-    command: sh -c 'echo testtest | ./mox setaccountpassword mjl@mox.example && ./mox serve'
+    tty: true # For job control
+    command: sh -c 'export MOXCONF=mox.conf; set -m; mox serve & sleep 1; echo testtest | mox setaccountpassword mjl@mox.example; fg'
     healthcheck:
       test: netstat -nlt | grep ':1143 '
       interval: 1s