Before that 'open-connection' would return #f, and thus
'current-services' would return a single #f value when its continuation
expects two.
Reported by calher on #guix.
* gnu/services/herd.scm (open-connection): Rethrow system-error
exceptions.
(with-shepherd): Expect CONNECTION to always be true; remove useless
'dynamic-wind'.
* guix/scripts/system.scm (warn-on-system-error): New macro.
(upgrade-shepherd-services): Wrap body in 'warn-on-system-error'.
1d6b7d5847