SystemRemoteCommandAction: avoid exception swallowing[1]

This prevents, among other things, to correctly display the "Missing Capabilities"
alert in case a system does not have the script.run capability.

[1] http://en.wikipedia.org/wiki/Error_hiding
Fix datepicker time at xx:xx PM pre-filled with xx:xx AM inducing user to
enter the wrong time. (bnc#880936)

We transport the data in 24 format and only use 1-12 when displaying.
DatePicker::getHour(), even if it is a data class, is 1-12!
Use getHourOfDay() instead.