tests: Skip /umockdev-run/umockdev-record-null-roundtrip
tests: Skip /umockdev-run/umockdev-record-null-roundtrip

Running stat or any other program crashes in Gentoo's sandbox when
running umockdev-run. Skip this new test for the time being, to avoid a
package build failure.

Fixes #182

martinpitt/umockdev,martinpitt/umockdev,martinpitt/umockdev