bugfix. use public-hostname not public-ipv4

Amazon does not let you retrieve a public IP address or
hostname of a newly created instance by querying
 http://instance-data/latest/meta-data/public-ipv4
but
 http://instance-data/latest/meta-data/public-hostname

does work.

The script was failing from not being able to retreive the public ip
address and use it to configure the tunnel
typo
add safeguard against running server script locally
add script to create VPN
docs describe locally installing boto