Testconfig: Set available android toolchain version for Qt5 projects

Android default toolchain version will be updated to 4.8, but ci is
only having version 4.7. Added configure option to use that until
nodes will get updated.

Change-Id: I8bc20f15e63b41d5c5658b648d2144daaaec2ee2
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>