mpich: Disable RPATH to avoid issues in package_qa

Set --disable-rpath to extra opts in order to avoid issues
in package_qa also change default pm to gforker because
hydra has problems with RPATH.

TODO: Make a patch for solve hydra rpath issues.

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>