Don't run __sleep when serializing objects for the debugger wire protocol

Summary: Running __sleep while serializing objects for the debugger can break
the protocol, e.g., if a breakpoint is hit while generating a backtrace.  It
seems doubtful that the user of the debugger actually wants to trigger __sleep
via debugger commands.

Reviewed By: @markw65

Differential Revision: D1519537
fix test

Summary: I'm so angry at you@​aravind for ruining such a good test day.

https://www.facebook.com/pxlcld/lxd9

Reviewed By: @alexmalyshev

Differential Revision: D1521427