oe-selftest: devtool: use assertRegex to match test output for meson
Replace strict string matching with assertRegex to allow for flexible
whitespace in the "Fail: 0" output from meson tests. This improves test
robustness against formatting changes.
This issue was discovered with scarthgap.
Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com> Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>