Add coverage of clean function in crypto_util
Add coverage of clean function in crypto_util

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