discovery: Fix deadlock between Close() and checkHealthCheckTimeout().
discovery: Fix deadlock between Close() and checkHealthCheckTimeout().

mattharden/vitess,erzel/vitess,vitessio/vitess,pivanof/vitess,davygeek/vitess,pivanof/vitess,tirsen/vitess,alainjobart/vitess,rnavarro/vitess,vitessio/vitess,mattharden/vitess,applift/vitess,sougou/vitess,applift/vitess,tirsen/vitess,pivanof/vitess,pivanof/vitess,tirsen/vitess,mapbased/vitess,rnavarro/vitess,tinyspeck/vitess,mattharden/vitess,dumbunny/vitess,mattharden/vitess,enisoc/vitess,alainjobart/vitess,HubSpot/vitess,alainjobart/vitess,sougou/vitess,vitessio/vitess,mahak/vitess,enisoc/vitess,mattharden/vitess,vitessio/vitess,mapbased/vitess,applift/vitess,rnavarro/vitess,dumbunny/vitess,davygeek/vitess,erzel/vitess,sougou/vitess,applift/vitess,erzel/vitess,mapbased/vitess,mattharden/vitess,dumbunny/vitess,applift/vitess,mahak/vitess,davygeek/vitess,mapbased/vitess,alainjobart/vitess,dcadevil/vitess,tirsen/vitess,mattharden/vitess,dumbunny/vitess,HubSpot/vitess,enisoc/vitess,applift/vitess,alainjobart/vitess,HubSpot/vitess,pivanof/vitess,mahak/vitess,enisoc/vitess,mapbased/vitess,mapbased/vitess,alainjobart/vitess,sougou/vitess,applift/vitess,mahak/vitess,applift/vitess,mapbased/vitess,dumbunny/vitess,rnavarro/vitess,dumbunny/vitess,tinyspeck/vitess,erzel/vitess,enisoc/vitess,tirsen/vitess,tinyspeck/vitess,HubSpot/vitess,alainjobart/vitess,dumbunny/vitess,dcadevil/vitess,mahak/vitess,mahak/vitess,dcadevil/vitess,sougou/vitess,enisoc/vitess,HubSpot/vitess,alainjobart/vitess,dumbunny/vitess,erzel/vitess,tirsen/vitess,pivanof/vitess,enisoc/vitess,vitessio/vitess,vitessio/vitess,davygeek/vitess,dcadevil/vitess,tirsen/vitess,tinyspeck/vitess,applift/vitess,pivanof/vitess,mapbased/vitess,erzel/vitess,pivanof/vitess,mahak/vitess,mattharden/vitess,mattharden/vitess,rnavarro/vitess,HubSpot/vitess,rnavarro/vitess,HubSpot/vitess,dcadevil/vitess,rnavarro/vitess,mahak/vitess,vitessio/vitess,rnavarro/vitess,dumbunny/vitess,dcadevil/vitess,mapbased/vitess,sougou/vitess,tinyspeck/vitess,applift/vitess,dumbunny/vitess,erzel/vitess,davygeek/vitess,pivanof/vitess,tirsen/vitess,tirsen/vitess,sougou/vitess,mattharden/vitess,vitessio/vitess,dcadevil/vitess,erzel/vitess,erzel/vitess,sougou/vitess,tinyspeck/vitess,davygeek/vitess,HubSpot/vitess,rnavarro/vitess,tinyspeck/vitess,erzel/vitess,davygeek/vitess,mapbased/vitess