Support more linux distributions

[unclev]

As of April, 25, 2020 trunk is not updated in Ubuntu 16.04.

Distro	stable	0.9	0.10	0.11	trunk
Ubuntu 16.04 xenial	0.11.5-1~xenial6	1nightly294-1~xenial	1nightly500-1~xenial	2020-04-24: 1nightly87-1~xenial	2020-03-24: 1nightly1241-1~xenial
Ubuntu 18.04 bionic	0.11.5-1~bionic6	1nightly294-1~bionic	1nightly500-1~bionic	1nightly87-1~bionic	1nightly1263-1~bionic
Ubuntu 19.04 disco	0.11.4-1~disco1	N/A	N/A	1nightly71-1~disco	1nightly1210-1~disco
Ubuntu 19.10 eoan	0.11.5-1~eoan6	N/A	N/A	1nightly87-1~eoan	1nightly1263-1~eoan
Ubuntu 20.04 focal	0.11.5-1~focal6	N/A	N/A	1nightly87-1~focal	1nightly1263-1~focal

To see available, installed, and upgradable prosody versions in the image, execute (eg. for trunk):

docker run --rm --user root unclev/prosody-docker-extended:trunk bash -c \
"apt update -qq && apt search prosody && apt list --upgradable | grep prosody"

As a partial solution: use Ubuntu 20.04 for trunk to be latest.

TODO: create images for the currently supported linux distributions from the Prosody package repository.

[unclev]

Ubuntu xenial, disco, eoan are not supported anymore. Update as soon as possible!