Avoid the same hostname in one session

By adding a # in front of used words, genhost will not display
the same word in two subsequent runs. It is however possible to
display the same word within one run. When generating a large
number of hosts, it might be hard to notice the duplication.
This commit solves this issue by re-reading the wordlist in each
iteration. I do not notice any significant slow-down, as reading
the wordlist hits the OS cache.

Signed-off-by: Jonas Eriksson <zqad@acc.umu.se>