Fix SDK environment setting

Since the change to use a meta-environment canadian package in the
OE-Core, the SDK environment setting has been broken. This uses the
new subscript environment to fix it and also move the environment
generation to the nativesdk-qtbase recipe.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
nativesdk-qtbase: make it possible to keep additional libraries

In some usecases for the nativesdk, you might need some build tools that are built upon Qt5. This means
that we're having a need to keep more of the libraries build by nativsdk-qtbase. This patch adds the
infrastructure to support that

Signed-off-by: Anders Darander <anders@chargestorm.se>