The earlier[*] fdopen/GreenPipe workaround is ineffective in nova, since
it uses the wrong guard predicate. Nova doesn't monkey_patch `os`, so
this change switches to checking against `socket` module instead.
Neither of these is strictly "correct" for our os.pipe/fdopen case, but
we just want to get some indication of "is eventlet being used".
[*] fdopen change: I4a6c0d4247aca17536316fb0ab163241ad545b20
Change-Id: I2bba4c45a66f49d5014f218a0ce24f221c9196bd