don't blow away mkspecs/modules-inst when reconfiguring

don't blow away mkspecs/modules-inst when reconfiguring

otherwise we get lots of nasty warning messages about missing pri files.

it is arguable whether it is a good idea to do that, but we preserve
mkspecs/modules, too, and the previously built libraries don't just
vanish, either.

Change-Id: Ieded8d8858f1b0135bc3bea894b4a676024ac8ca
Reviewed-by: Girish Ramakrishnan <girish.1.ramakrishnan@nokia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>
Reviewed-by: Marius Storm-Olsen <marius.storm-olsen@nokia.com>