Sdk Fixes

Hi,

could somone comment on my patch series:

To get the nativesdk package compiled you need the patch for the nativesdk-dbus recipe to not depend on nativesdk-dubs-ptest-ptest which is already submitted to oe-core.

Current outstanding work is:
 - Calculate the relative paths from the install directories
 - Move the qt.conf generation into the nativesdk package, because we can't depend on target packages from there


Some notes on why i did it this way:

It is very important to use the mkspecs from the target sysroot because all the modules built for the target are installing special files there which are needed for proper cross compilation.
The trick is to just use the mkspecs from the target sysroot.

Is it ok to enable the nativesdk-qtbase by appending nativesdk-packagegroup-sdk-host ?

Is it ok to change the default dev packages (from qt5.inc) to include the mkspecs ?
If not how can i guarantee that the mkspecs are installed int the sysroot. 

Best Regards
 Dominik

P.S.: I hope it is ok to send the pull request this way, the oe-core script doesn't work for me somehow