Make possible to search conf files from subdirectories automatically

With this change one can put conf files like e.g.

/configurations/linux/x86/qt520-conf
/configurations/linux/x64/qt520-conf
/configurations/linux/my_component_x/x86/enginio-conf

etc.

The filenames still need to be unique.

Change-Id: I14b7c6da58a7b6618e1f6786a87e6160967caec6
Reviewed-by: Samuli Piippo <samuli.piippo@digia.com>
Reviewed-by: Antti Kokko <antti.kokko@digia.com>