Fix memory leaks in soft-pkcs11 code

Fix memory leaks in soft-pkcs11 code

Fix leaks detected by asan in t_pkinit.py.  Add a helper to free a
struct st_object and free objects in C_Finalize().  Duplicate the X509
cert in add_certificate() instead of creating aliases so it can be
properly freed.  Start the session handle counter at 1 so that
C_Finalize() won't confuse the first session handle with
CK_INVALID_HANDLE (defined to 0 in pkinit.h) and will properly clean
the session object.