cp mod: honor `env` argument in list_master() & hash_file()

************* Module salt.modules.cp
salt/modules/cp.py:441: [W0613(unused-argument), list_master] Unused argument 'env'
salt/modules/cp.py:548: [W0613(unused-argument), hash_file] Unused argument 'env'
Merge pull request #8999 from hulu/cp-env

cp mod: honor `env` argument in list_master() & hash_file()