pillowfight.cc: fix leaking event loop descriptors

==31400== FILE DESCRIPTORS: 4 open at exit.
==31400== Open file descriptor 3:
==31400==    at 0x5AD6047: epoll_create1 (syscall-template.S:82)
==31400==    by 0x638BC9C: epoll_init (ev_epoll.c:239)
==31400==    by 0x638CED1: loop_init (ev.c:2610)
==31400==    by 0x638D67B: ev_loop_new (ev.c:2787)
==31400==    by 0x6186829: lcb_create_libev_io_opts (plugin-libev.c:399)
==31400==    by 0x4E46B57: create_v1 (iofactory.c:232)
==31400==    by 0x4E46A73: create_v0 (iofactory.c:198)
==31400==    by 0x4E469A4: lcb_create_io_ops (iofactory.c:172)
==31400==    by 0x404F20: ThreadContext::ThreadContext(unsigned long) (pillowfight.cc:278)
==31400==    by 0x40417D: main (pillowfight.cc:592)

Change-Id: I8b30d6b0a6e778918be4ec2efed780393a2c4ad4
Reviewed-on: http://review.couchbase.org/25082
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>