When an operator runs `source overcloudrc` then `source stackrc`,
ENV['no_proxy'] keep having overcloud information because stackrc
doesn't include no_proxy line.
If they runs deploy commands like overcloud deploy with that situation,
the command is executed with ENV['no_proxy'] including overcloud hosts.
This generates overcloudrc with duplicated host in no_proxy line,
because no_proxy in overcloudrc is generated by joining ENV['no_proxy']
and rquired overcloud hosts.
This patch makes sure that duplicated hosts are removed before they get
dumped into no_proxy parameter.
(cherry picked from commit