Change absolute path to relative path for some variables in ERT

[tayloris]

When we render each Eclipse/OPM simulation file for each realization we require several file name arguments that are currently absolute paths.

Each realization is to be render inside OUTPUT_FOLDER/output/runpath/realization-*/iter-*, and the files we need to pass as arguments live in OUTPUT_FOLDER/.

I removed the absolute path and include "../../../../" to point towards the corresponding parent directory.

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Contributor checklist

• [x] :tada: This PR closes #274.
• [x] :scroll: I have broken down my PR into the following tasks:
  • [x] Change absolute paths to relative path

[wouterjdb]

274 is no longer an open issue.