go/fixchain: remove data races in unit test
go/fixchain: remove data races in unit test

RJPercival/certificate-transparency,lexibrent/certificate-transparency,phad/certificate-transparency,lexibrent/certificate-transparency,pphaneuf/certificate-transparency,RJPercival/certificate-transparency,grandamp/certificate-transparency,pphaneuf/certificate-transparency,RJPercival/certificate-transparency,pphaneuf/certificate-transparency,grandamp/certificate-transparency,phad/certificate-transparency,grandamp/certificate-transparency,RJPercival/certificate-transparency,lexibrent/certificate-transparency,google/certificate-transparency,google/certificate-transparency,pphaneuf/certificate-transparency,google/certificate-transparency,phad/certificate-transparency,grandamp/certificate-transparency,lexibrent/certificate-transparency,google/certificate-transparency,phad/certificate-transparency