travis: set the installation prefix to /usr
travis: set the installation prefix to /usr

CMake defaults to /usr/local which results in libraries being installed in
/usr/local/lib. Unfortunately, this path isn't in the loader's default
locations.

The canonical installation path is /usr. /usr/local is recommended for stuff
not handled by the package manager but in the context of the CI, this isn't
relevant.

Signed-off-by: David Wagner <60228a510f9a76940848fa2d29321fc4edfc2119@intel.com>

geekboxzone/mmallow_external_parameter-framework,geekboxzone/mmallow_external_parameter-framework,geekboxzone/mmallow_external_parameter-framework