Simplify mod_global_distrib_SUITE:multi_connection:test_muc_conversation_history

[arcusfelis]

This PR addresses "Long tests are evil".

Proposed changes include:

• Helper functions

[mongoose-im]

7184.1 / Erlang 22.0 / small_tests / 6dd45e7
Reports root / small

---

7184.2 / Erlang 22.0 / internal_mnesia / 6dd45e7
Reports root/ big
OK: 1244 / Failed: 0 / User-skipped: 136 / Auto-skipped: 0

---

7184.3 / Erlang 22.0 / odbc_mssql_mnesia / 6dd45e7
Reports root/ big
OK: 3153 / Failed: 0 / User-skipped: 262 / Auto-skipped: 0

---

7184.4 / Erlang 22.0 / mysql_redis / 6dd45e7
Reports root/ big
OK: 3151 / Failed: 0 / User-skipped: 264 / Auto-skipped: 0

---

7184.5 / Erlang 22.0 / riak_mnesia / 6dd45e7
Reports root/ big
OK: 1470 / Failed: 0 / User-skipped: 145 / Auto-skipped: 0

---

7184.6 / Erlang 22.0 / ldap_mnesia / 6dd45e7
Reports root/ big
OK: 1213 / Failed: 0 / User-skipped: 167 / Auto-skipped: 0

---

7184.9 / Erlang 21.3 / pgsql_mnesia / 6dd45e7
Reports root/ big / small
OK: 3166 / Failed: 0 / User-skipped: 249 / Auto-skipped: 0

[NelsonVides]

I'm happy with the changes, it looks cool, but I don't see any test getting any faster :/
From master: https://circleci-mim-results.s3.eu-central-1.amazonaws.com/branch/master/4591/mysql_redis.2207/big/ct_run.test@default-69029517-4fba-4ccf-8833-2089d0258f99.2019-09-16_15.17.21/big_tests.tests.mod_global_distrib_SUITE.logs/run.2019-09-16_15.34.24/suite.log.html
From PR: https://circleci-mim-results.s3.eu-central-1.amazonaws.com/PR/2457/4621/mysql_redis.2207/big/ct_run.test@default-e1bdfa33-6c24-401d-b4c9-f9bab770d650.2019-09-16_15.37.41/big_tests.tests.mod_global_distrib_SUITE.logs/run.2019-09-16_15.55.57/suite.log.html
🙁

[arcusfelis]

I'm happy with the changes, it looks cool, but I don't see any test getting any faster :/
From master: https://circleci-mim-results.s3.eu-central-1.amazonaws.com/branch/master/4591/mysql_redis.2207/big/ct_run.test@default-69029517-4fba-4ccf-8833-2089d0258f99.2019-09-16_15.17.21/big_tests.tests.mod_global_distrib_SUITE.logs/run.2019-09-16_15.34.24/suite.log.html
From PR: https://circleci-mim-results.s3.eu-central-1.amazonaws.com/PR/2457/4621/mysql_redis.2207/big/ct_run.test@default-e1bdfa33-6c24-401d-b4c9-f9bab770d650.2019-09-16_15.37.41/big_tests.tests.mod_global_distrib_SUITE.logs/run.2019-09-16_15.55.57/suite.log.html
🙁

it shouldn't go any faster, it's just making that specific test more readable.