Eradicate relative paths for small tests

[arcusfelis]

Use PWD variable in small_path_helper module
Simplify include statements

[codecov-io]

Codecov Report

Merging #1768 into master will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1768      +/-   ##
==========================================
+ Coverage   74.38%   74.53%   +0.15%     
==========================================
  Files         289      289              
  Lines       26869    27166     +297     
==========================================
+ Hits        19986    20248     +262     
- Misses       6883     6918      +35

Impacted Files	Coverage Δ
src/rdbms/mongoose_rdbms_odbc.erl	84.78% <0%> (-8.08%)	⬇️
...rc/global_distrib/mod_global_distrib_transport.erl	47.05% <0%> (-5.89%)	⬇️
src/mod_push_service_mongoosepush.erl	88.23% <0%> (-5.89%)	⬇️
src/mod_mam_utils.erl	84.93% <0%> (-2.45%)	⬇️
...c/global_distrib/mod_global_distrib_server_mgr.erl	78.87% <0%> (-1.41%)	⬇️
src/mod_muc_log.erl	77.69% <0%> (ø)	⬆️
src/mod_roster.erl	79.16% <0%> (+0.24%)	⬆️
src/node_flat.erl	74.3% <0%> (+0.3%)	⬆️
src/mod_mam_muc_odbc_arch.erl	83.83% <0%> (+0.77%)	⬆️
src/mod_bosh_socket.erl	81.66% <0%> (+1%)	⬆️
... and 5 more

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