Fix flaky MX test
Fix flaky MX test

Fix the flakyness by checking for 'a' or 'b'. Admittedly this is a
cross hack.

Fixes #189

loveshell/skydns,tuannvm/skydns,ZeaLoVe/skydns,netf/skydns,nicescale/skydns,tonicbupt/skydns,zhang0137/skydns,hw-qiaolei/skydns,vinhhrv/skydns,skynetservices/skydns,yonglehou/skydns,weekface/skydns,AdoHe/skydns,no2key/skydns