Fix permissions of /usr/local/bin

Currently, the permissions in the containers look somewhat like this:

build@127f77976b47:/usr/local/bin> ls -la
total 180
drwxr-xr-x 1 build build  4096 May 24 12:36 .
drwxr-xr-x 1 root  root   4096 May 24 12:36 ..
drwxr-xr-x 8 root  root   4096 May 24 12:36 .git
-rw-r--r-- 1 root  root     30 May 24 12:36 .gitignore

Since a recent Git security update, this results in the following error when doing git pull (in icinga-build-entrypoint in this repo):

fatal: unsafe repository ('/usr/local/bin' is owned by someone else)

This can be fixed by making /usr/local/bin owned by root as well.

Task: remove chown build.build /usr/local/bin from all Dockerfiles.