introduce app.intaddrs which are ec2 secondary IPs

requires introduction of app.azlimit which limits the availability zones
for an instance / autoscale group to a single AZ.  Subnets cannot span
AZs, so this is the only option.

ec2rotatehosts now detects the first secondary address and preserves it
Merge pull request #18 from WrathOfChris/cm-ec2secondaryaddrs

introduce app.intaddrs which are ec2 secondary IPs