credit: Update other parameters when setting tslice_ms

credit: Update other parameters when setting tslice_ms

Add a utility function to update the rest of the timeslice
accounting fields when updating the timeslice of the
credit scheduler, so that capped CPUs behave correctly.

Before this patch changing the timeslice to a value higher
than the default would result in a domain not utilizing
its full capacity and changing the timeslice to a value
lower than the default would result in a domain exceeding
its capacity.

Signed-off-by: Nate Studer <nate.studer@dornerworks.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>