Fixes a regression introduced in
977eb5d023 whereby file system services
would now have a different name.
* gnu/services/base.scm (file-system->shepherd-service-name): Revert
changes introduced in 977eb5d023.
* gnu/services/shepherd.scm (%store-characters): New variable
(shepherd-service-file-name): Map all the characters outside
%STORE-CHARACTERS to #\-.