packaging: add Cosmic and Disco, remove Trusty and Artful
- Trusty was publicly supported until 2019-04-30
- Artful was publicly supported until 2018-07-19
- Cosmic was publicly supported until 2019-07-18
- Disco will be publicly supported until 2020-01
Cosmic is officially out-of-date, but since it still may be in use, and because
we didn't add it when it first came out, I think it would be nice to support it
until the next time somebody decides to update this list of Ubuntu releases.
Differential Revision: https://phab.mercurial-scm.org/D6761
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed