c8330d4 qa: Use node.datadir instead of tmpdir in test framework (MarcoFalke)
Pull request description:
Commit c53c9831ee introduced the utility function `get_datadir_path`, however not all places in the code use this util function. Using the util function everywhere makes it easier to review pull requests related to the datadir.
This commit replaces datadir path creation with the `datadir` member of `TestNode`, which itself uses `get_datadir_path`.
Tree-SHA512: c75707ab7149d732a6d56152a5813138a33459d3d07577b60b89f2a207c83b7663fac5f203593677c9892d1c23a5eba4bd45c5c4ababf040d720b437240fcddf