Use the latest mongooseim-docker

[chrzaszcz]

• Config file updated to 'mongooseim.toml'
• Ubuntu version fixed at 18.04

This PR attempts to fix the issue of building MongooseIM on CircleCI with Ubuntu 16.04 and using the resulting tarball to build a docker image based on Ubuntu 20.04 - these two had incompatible library versions and recent MongooseIM docker images were not starting at all.

The two still don't align completely (16.04 and 18.04), but the image for this PR does not crash on startup.

Possibilities:

1. Run CircleCI on Ubuntu 20.04, upgrade Docker image to 20.04 - needs fixing multiple issues, see Update CircleCI machine to ubuntu-20.04 #2925
2. Run CircleCI on Ubuntu 18.04 in Docker (no machine for 18.04) - most likely even more difficult, but we could reduce the duplication between CI and Docker-related shell scripts and make them unified. Not sure about the performance.
3. Downgrade Docker image to use Ubuntu 16.04 - it might require least work, but it's a very short-term solution and the image for 16.04 does not have a nice tag at phusion/baseimage.
4. For now, make the circle-build-and-push-docker script build MongooseIM on the builder docker image. This would increase the duration of the CircleCI job by about 5 minutes (or more...)

[mongoose-im]

8692.1 / Erlang 23.0.3 / small_tests / a07542e
Reports root / small

---

8692.2 / Erlang 23.0.3 / internal_mnesia / a07542e
Reports root/ big
OK: 1494 / Failed: 0 / User-skipped: 165 / Auto-skipped: 0

---

8692.3 / Erlang 23.0.3 / odbc_mssql_mnesia / a07542e
Reports root/ big
OK: 2767 / Failed: 0 / User-skipped: 228 / Auto-skipped: 0

---

8692.5 / Erlang 23.0.3 / riak_mnesia / a07542e
Reports root/ big
OK: 1628 / Failed: 0 / User-skipped: 177 / Auto-skipped: 0

---

8692.7 / Erlang 23.0.3 / elasticsearch_and_cassandra_mnesia / a07542e
Reports root/ big
OK: 330 / Failed: 0 / User-skipped: 38 / Auto-skipped: 0

---

8692.4 / Erlang 23.0.3 / mysql_redis / a07542e
Reports root/ big
OK: 2762 / Failed: 0 / User-skipped: 233 / Auto-skipped: 0

---

8692.6 / Erlang 23.0.3 / ldap_mnesia / a07542e
Reports root/ big
OK: 1406 / Failed: 0 / User-skipped: 253 / Auto-skipped: 0

---

8692.9 / Erlang 22.3 / pgsql_mnesia / a07542e
Reports root/ big / small
OK: 2780 / Failed: 0 / User-skipped: 215 / Auto-skipped: 0

[DenysGonchar]

looks good