Before the profile commands would not run if a single package is
installed since `buildEnv` will produce a symlink directly to that
package. By adding this dummy package we ensure that a real directory
will be generated.
Fixes#1392
This change stops update-mime-database from running unless the
`share/mime/packages` directory is writable. For some reason it
appears to be read-only on WSL1.
Fixes#1192
