The library module introduced by commit 2cd13026e ("misc: move the RDT
interface to common library") was put under the library/ directory which is
not by default searchable from elementpath_overlay. This patch works around
the issue by adding that path to sys.path.
Also fix a typo in the RDT checking assertion.
Tracked-On: #6690
Signed-off-by: Junjie Mao <junjie.mao@intel.com>
