test: improve failure printing in /etc/hosts test
test: improve failure printing in /etc/hosts test

Previously if we missed a name we would get `Failure "List.combine"`
This patch will make the exception contain the expected number of
entries and the actual number.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit