Fix for issues #3581, #1481 and #7650:

Fix for issues #3581, #1481 and #7650:

1. The assumptions in check_node() were too restrictive:

     - Hardware addresses with universal_local_bit=1 are valid
       (locally administered).

     - Many of the tested functions (including uuid.getnode())
       may return valid RFC 4122 random node IDs. These are pretty
       much random 48-bit values with the multicast bit set to 1.

2. _unixdll_getnode() calls _uuid_generate_time(), which may be None
   on some platforms. The resulting TypeError is now caught.