Split out test helpers into package "restic/test"
Split out test helpers into package "restic/test"

byo/restic,fawick/restic,stuertz/restic,kurin/restic,middelink/restic,stuertz/restic,byo/restic,ckemper67/restic,jayme-github/restic,mappu/restic,bchapuis/restic,howeyc/restic,fawick/restic,ar-jan/restic,arithmetric/restic,ar-jan/restic,pombredanne/restic,intfrr/restic,restic/restic,kurin/restic,middelink/restic,episource/restic,jayme-github/restic,klauspost/restic,restic/restic