The cloud-init configuration runs on boot, which can result in a race
condition between that and service startup. This has caused provisioning
failures because Nomad expects the userdata to have configured a host volume
directory. Diagnosing this was also compounded by a warning being fired by
systemd for the Nomad unit file.
* Update the location of the `StartLimitIntervalSec` field to it's
post-systemd-230 location.
* Ensure that the weekly AMI build is up-to-date to reduce the risk of
unexpected system software changes.
* Move the host volume to a directory we can set up at AMI build time rather
than in userdata.
Newer EC2 instances are both cheaper and have generally better
performance.
The dnsmasq configuration had a hard-coded interface name, so in order to
accomodate instances with more recent networking that result in so-called
predictable interface names, the dnsmasq configuration needs to be replaced at
runtime with userdata to select the default interface.
* remove outdated references to envchain in documentation
* add new host volume locations in userdata
* don't exit the entire script during provisioning, just return
