discoverd/client: Fix intermittent TestFiltering test
discoverd/client: Fix intermittent TestFiltering test

This fixes a race condition where the watchSet has received the
discoverd update but the filtered set hasn't, leading to set.Services()
only returning one service and the test failing.

Signed-off-by: Lewis Marshall <748e1641a368164906d4a0c0e3965345453dcc93@lmars.net>

shads196770/flynn,schatt/flynn,tonicbupt/flynn,pkdevbox/flynn,whouses/flynn,supermario/flynn,arekkas/flynn,supermario/flynn,Brandywine2161/flynn,justintung/flynn,shutej/flynn,pkdevbox/flynn,whouses/flynn,whouses/flynn,supermario/flynn,josephglanville/flynn,technosophos/flynn,schatt/flynn,felixrieseberg/flynn,GrimDerp/flynn,philiplb/flynn,lmars/flynn,pkdevbox/flynn,tonicbupt/flynn,lmars/flynn,GrimDerp/flynn,mubassirhayat/flynn,rikur/flynn,supermario/flynn,jzila/flynn,pkdevbox/flynn,jzila/flynn,shads196770/flynn,Brandywine2161/flynn,schatt/flynn,Brandywine2161/flynn,justintung/flynn,pkdevbox/flynn,lmars/flynn,benbjohnson/flynn,tonicbupt/flynn,technosophos/flynn,TribeMedia/flynn,rikur/flynn,GrimDerp/flynn,josephglanville/flynn,schatt/flynn,TribeMedia/flynn,arekkas/flynn,clifff/flynn,pkdevbox/flynn,technosophos/flynn,benbjohnson/flynn,philiplb/flynn,justintung/flynn,schatt/flynn,rikur/flynn,benbjohnson/flynn,josephglanville/flynn,felixrieseberg/flynn,arekkas/flynn,whouses/flynn,whouses/flynn,lmars/flynn,tonicbupt/flynn,whouses/flynn,philiplb/flynn,kgrz/flynn,clifff/flynn,benbjohnson/flynn,Brandywine2161/flynn,TribeMedia/flynn,kgrz/flynn,ozum/flynn,clifff/flynn,mubassirhayat/flynn,ozum/flynn,lmars/flynn,felixrieseberg/flynn,Brandywine2161/flynn,clifff/flynn,shads196770/flynn,jzila/flynn,flynn/flynn,flynn/flynn,mubassirhayat/flynn,kgrz/flynn,kgrz/flynn,benbjohnson/flynn,shads196770/flynn,TribeMedia/flynn,GrimDerp/flynn,philiplb/flynn,ozum/flynn,GrimDerp/flynn,josephglanville/flynn,justintung/flynn,shads196770/flynn,ozum/flynn,TribeMedia/flynn,josephglanville/flynn,kgrz/flynn,jzila/flynn,benbjohnson/flynn,josephglanville/flynn,schatt/flynn,flynn/flynn,felixrieseberg/flynn,clifff/flynn,philiplb/flynn,kgrz/flynn,clifff/flynn,felixrieseberg/flynn,tonicbupt/flynn,justintung/flynn,GrimDerp/flynn,flynn/flynn,rikur/flynn,Brandywine2161/flynn,rikur/flynn,ozum/flynn,justintung/flynn,flynn/flynn,rikur/flynn,supermario/flynn,technosophos/flynn,TribeMedia/flynn,mubassirhayat/flynn,supermario/flynn,ozum/flynn,arekkas/flynn,technosophos/flynn,shads196770/flynn,jzila/flynn,arekkas/flynn,jzila/flynn