Various customisations:

* Use sh instead of bash as bash not installed in boot2docker.
* Provide the value of $GUESTNAME as an argument to the DHCP client so the DHCP server can add it to DNS (if the DHCP server is also acting as a DNS server, e.g. dnsmasq).
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Spelling mistake.
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Correction for grammatical error.
Merge pull request #74 from jimmcslim/master

Various customisations; add $GUESTNAME as parameter to dhcp client request.