examples/ct: allow multiple CA-roots files (#527)
examples/ct: allow multiple CA-roots files (#527)

This makes it easier to run variant configurations, e.g. a
test server with the base set of roots plus an extra testing root.

RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,RJPercival/certificate-transparency-go,daviddrysdale/certificate-transparency-go,google/certificate-transparency-go,daviddrysdale/certificate-transparency-go,RJPercival/certificate-transparency-go,google/certificate-transparency-go