Unit tests for store.py: rename_submission OSError exception handling flow
Unit tests for store.py: rename_submission OSError exception handling flow

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