10-tls-deploy causes failure in certain scenarios

[lazypower]

tests/10-tls-deploy was intended to be a baseline validation for the tls layer. This however is hard-coded to series=trusty, and causes the etcd test suite to fail because the ETCD charm will not receive resources when its deployed on trusty as a local charm.

We either need to make the series a configurable parameter, we should bump this up to xenial, or it should be omitted and instead ship with some boilerplate testing that users can include in their tests if TLS certificate validation is important in their testing routines.

this is a limited shelf-life issue, with limited scope. This goes away if amulet grows support to publish resources for a charm.