Qnx: Support multiple BlackBerry target configurations

The new bbndk 10.2 is based on multiple targets (based on multiple bbnk-env scripts).
There is no default/common bbnk-env.sh file anymore, and an NDK directory may contain
various bbndk-env scripts (i.e targets).

This patch makes the BlackBerryConfiguration based on the bbnk-env script path
rather than on the NDK path. This will enable having multiple configurations
per targets in the same NDK directory.

N.B: NDKs 10.1 with one default bbnk-env file are still supported.

Change-Id: Icec57c6e722caec7e5ff81e3a9ce4d2cf11f249a
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Nicolas Arnaud-Cormos <nicolas@kdab.com>