Dockerize LDAP

[arcusfelis]

This PR addresses "Travis scripts are too travis specific".

Proposed changes include:

• LDAP running in docker container
• Make docker-volume logic generic

[codecov]

Codecov Report

Merging #1899 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1899      +/-   ##
==========================================
- Coverage   74.59%   74.57%   -0.02%     
==========================================
  Files         307      307              
  Lines       28135    28135              
==========================================
- Hits        20988    20983       -5     
- Misses       7147     7152       +5

Impacted Files	Coverage Δ
...rc/global_distrib/mod_global_distrib_transport.erl	47.05% <0%> (-5.89%)	⬇️
src/mod_push_service_mongoosepush.erl	82.85% <0%> (-5.72%)	⬇️
src/mod_muc_log.erl	77.69% <0%> (-0.77%)	⬇️
...c/global_distrib/mod_global_distrib_server_mgr.erl	82.39% <0%> (-0.71%)	⬇️
src/eldap_utils.erl	53.95% <0%> (+0.71%)	⬆️
...bal_distrib/mod_global_distrib_hosts_refresher.erl	84.78% <0%> (+2.17%)	⬆️

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[ludwikbukowski]

approve (working on my OS X machine locally)