Move saving of hosts file to after all ports are forwarded

[rmja]

This fixes #74

[cjimti]

@rmja Thank you for working on this. I can take a deeper look at it this coming weekend. I have some things to contemplate. Some people would like kubefwd to monitor connections and re-connect on pod failures, which would mean removing and adding new entries through the duration of the run. In other circumstances, some people on my team do not want to wait till all forwards have completed before they can start accessing services that have begun their forward (we have some namespaces with hundreds of services.) There is another ticket asking for a feature to monitor a namespace and forward any new services. These conditions all make the case for keeping isolated writes to /etc/hosts. I am hoping that I can think of a workable compromise.

[rmja]

Year, I can see the conflict. How about assigning IP's and writing the hosts file up front, and then actually map the services afterwards?

[cjimti]

@rmja I am going to merge this and test a few adjustments. I need to work on #75 which is somewhat related in that kubefwd does not reload the state of /etc/hosts before removing entries and saving, therefore saving over any entries added by other processes while kubefwd is sunning.

[cjimti]

In relase 1.9.1

I split the difference. The initial write to `/etc/hosts/' happens after all the forwards have completed (per your PR) however I need to reload and save when exiting each routine to fix #75.

Thank you for your contribution!