Renamed some docker files to Dockerfile

This makes it simpler to manage by using the default name. It also helps
my editor to recognise the file and highlight it properly.

docker/1_base/build.sh

@@ -1,4 +1,4 @@
 #!/usr/bin/env bash
 
 # Uses --no-cache to always get the latest upstream (security) upgrades.
-exec docker build --no-cache "$@" -t pillar_base -f base.docker .
+exec docker build --no-cache "$@" -t pillar_base .