Move all path related functions into path_helper in big tests

[arcusfelis]

This PR is continuation of #1626

Proposed changes include:

• new helper module path_helper
• new env variables REPO_DIR and TEST_DIR passed to VM, running the big tests

[codecov-io]

Codecov Report

Merging #1760 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1760      +/-   ##
==========================================
+ Coverage    74.6%   74.62%   +0.01%     
==========================================
  Files         283      283              
  Lines       26578    26578              
==========================================
+ Hits        19829    19834       +5     
+ Misses       6749     6744       -5

Impacted Files	Coverage Δ
src/mod_bosh.erl	93.27% <0%> (-1.69%)	⬇️
src/ejabberd_c2s.erl	84.86% <0%> (+0.15%)	⬆️
src/mod_roster.erl	79.16% <0%> (+0.24%)	⬆️
src/mod_mam_muc_odbc_async_pool_writer.erl	73.98% <0%> (+3.25%)	⬆️

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[erszcz]

We have a readlink.sh file stating that it's needed for MacOS - how does this change work on Mac?

[arcusfelis]

Lovely, was thinking about this

function readlink() {
  DIR=$(echo "${1%/*}")
  (cd "$DIR" && echo "$(pwd -P)")
}

[erszcz]

I don't know which is better: readlink.sh that we have in the repo or your proposed function, but I bet you can work it out :)

[arcusfelis]

This script looks broken. I will add another one into tools.

./readlink.sh ../                                                          
/home/user/erlang/esl/2017/MongooseIM/.. 

[arcusfelis]

done

[fenek]