This ensures that 'urandom-seed' is started before programs that rely on
sources of randomness.
Fixes <https://bugs.gnu.org/29773>.
Reported by Leo Famulari <leo@famulari.name>.
* gnu/services/base.scm (urandom-seed-shepherd-service): Change
'requirement' to (file-systems).
(urandom-seed-service-type): Extend USER-PROCESSES-SERVICE-TYPE.