Add ARM64 CI to Travis

Add ARM64 CI to Travis

We need to install a number of additional packages that are installed
by default on the AMD64 workers.

We also have to manually set up the MySQL user.

For now we don't set up Postgres -- if anyone wants to figure that
out, it would be great ;)

Log redirections in compile.sh are removed, because /dev/stdout is
not accessible. We don't see to use this anyway.