Python binding should look for couchstore.dll

The new CMake based build outputs the couchstore library as
couchstore.dll rather than libcouchstore-1.dll

Change-Id: I70c9c2e7e77ad5c9c40d1ec80d63675875caf114
Reviewed-on: http://review.couchbase.org/32541
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>