Support the definition of the `.ini` file by defining an absolute filepath in `_SQUASH_TF_TESTCASE_PARAM_FILES`

In order to properly solve orchestrator#178 (closed) (we will provide a workaround for the time being), the java-param-library should support the definition of the .ini file by an absolute path.
The current behavior (defining the .ini file by a path relative to the current working directory) must still work.

Note: Path.resolve seems a way to easily implement this.