iopipe: fix leak of streams
iopipe: fix leak of streams

g_simple_io_stream_new() do not steal references from us, unref the
streams to avoid the leaks.

Leak found by Victor Toso.

==30787== 2,808 (648 direct, 2,160 indirect) bytes in 9 blocks are definitely lost in loss record 479 of 482
==30787==    at 0x93AEBFD: g_type_create_instance (gtype.c:1849)
==30787==    by 0x939128A: g_object_new_internal (gobject.c:1774)
==30787==    by 0x9392AA0: g_object_newv (gobject.c:1921)
==30787==    by 0x939338B: g_object_new (gobject.c:1614)
==30787==    by 0x403B30: make_gio_pipe (giopipe.c:441)
==30787==    by 0x403C8E: spice_make_pipe (giopipe.c:465)
==30787==    by 0x4029B5: fixture_set_up (pipe.c:42)
==30787==    by 0x9844EC8: test_case_run (gtestutils.c:2123)
==30787==    by 0x9844EC8: g_test_run_suite_internal (gtestutils.c:2185)
==30787==    by 0x984509A: g_test_run_suite_internal (gtestutils.c:2196)
==30787==    by 0x98453FA: g_test_run_suite (gtestutils.c:2249)
==30787==    by 0x9845430: g_test_run (gtestutils.c:1553)
==30787==    by 0x402012: main (pipe.c:312)

SPICE/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk