Fix permissions when running dev container as non-root user

I wanted to pass `—user` to `docker-compose` up, but that option doesnt exist. To get around this, I had to record the uid on the host (CURRENT_UID), interpolate the variable in tools/docker-compose.yml, and detect that inside the container. I then piggy-backed on the /etc/passwd hack we use for scenarios with unpredictable uids.

tools/docker-compose.yml

@@ -2,6 +2,7 @@ version: '2'
 services:
   # Primary AWX Development Container
   awx:
+    user: ${CURRENT_UID}
     image: ${DEV_DOCKER_TAG_BASE}/awx_devel:${TAG}
     hostname: awx
     environment: