Fix dnsmasq package install failure

* added gettext to quantum_dhcp_build_packages, or it throws 'ERROR xgettext: Command not found'
* made dnsmasq_all to be installed last to fix install failure due to version dependency on dnsmasq-base(>= 2.65-1)
* added gettext to test example in dhcp_agent_spec.rb

Change-Id: I4f3f113d0b3cb182d52b0df763eb329d07a20166
Merge "Fix dnsmasq package install failure"