Stups-senza

- 288: fix traffic switch
- 287: depend on `typing` module (even for Python 3.5+)

- 197: use Alias records instead of CNAMEs

TL;DR: Senza v2.0.96+ internally now manages “Alias” DNS records instead of CNAMEs. Behavior of traffic switching generally stays the same, but you will see differences in the output of DNS tools like dig or host.

The new Senza version v2.0.96+ will introduce a major change in how DNS records and traffic switching is handled:
- Route 53 DNS records are now Alias instead of CNAME records pointing to the ELB
DNS lookups (e.g. “dig foo.myteam.zalan.do”) will no longer “reveal” the stack version as Route 53 directly returns A records (ELB IPs):


dig output for Senza 1.0.92 with CNAMEs
foo.myteam.example.org. 20 IN CNAME foo-cd72c1-1849488195.eu-central-1.elb.amazonaws.com.

- 281: pass `--region` to ACM

- 279: fix SSL cert lookup if one of the ACM certs has status `VALIDATION_TIMED_OUT`

- 274: make ASG `MetricType` optional

- 277: allow HTTP-only ELBs by overwritting `Listeners` and by ignoring `SSLCertificateId`