Avoid skipping python tests for 3rd party ext libraries in CMake builds

Currently the python unit test framework expects to find extension modules under the libtool build path '.libs'. CMake doesn't export its built libraries under a '.libs' sub-directory.

e.g.

CMake

ext/compressors/snappy/libwiredtiger_snappy.so

Libtool:

ext/compressors/snappy/.libs/libwiredtiger_snappy.so

Update the python unit test framework to also detect the library outside of the '.libs' sub-directory.