eunit fixes and improvements

[c-bik]

This PR is to adapt to error interface change to PR #109 Test erlang compile warning fixes Dead code in eunit test removed added missing in file and line into to dpiContext_create

TBD by @KarlKeiser

• Please fix the following two error message in this branch (replace the text with something meaning ful) https://github.com/K2InformaticsGmbH/oranif/blob/6e3deec7656e93f2873d0f6113c38319e8bb950b/test/oranif_eunit.erl#L444 https://github.com/K2InformaticsGmbH/oranif/blob/6e3deec7656e93f2873d0f6113c38319e8bb950b/test/oranif_eunit.erl#L576
• I removed some dead code in erlang eunit, please make sure that it did NOT effect coverage!

@acautin after you merge this PR to yours the travis test should go through again.