Bug 31112: (follow-up) Bring back the check for non-priority holds

Bug 31112: (follow-up) Bring back the check for non-priority holds

Before the changes from bug 31112 when CheckReserves returned a
non-priority hold we didn't return "on_reserve" status but checked in
addition to that whether there are any priority holds and if there
were, only then we returned the "on_reserve" error.

Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>