tests: verbose teardown to debug #844 (take 2)
tests: verbose teardown to debug #844 (take 2)

The previous find is misplaced: it will just show the temporary dir is
populated. What we really need to know is what it contains *after*
rmtree failed and not before.

conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,micahflee/securedrop,ehartsuyker/securedrop,ehartsuyker/securedrop,micahflee/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,heartsucker/securedrop,heartsucker/securedrop,micahflee/securedrop,ehartsuyker/securedrop,conorsch/securedrop,conorsch/securedrop,garrettr/securedrop,garrettr/securedrop,conorsch/securedrop,conorsch/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,garrettr/securedrop,micahflee/securedrop