manif: fix loading rock manifest from the correct repo
manif: fix loading rock manifest from the correct repo

get_providing_file was always loading the rock_manifest from the
default repo.

luarocks/luarocks,tarantool/luarocks,tarantool/luarocks,luarocks/luarocks,keplerproject/luarocks,luarocks/luarocks,keplerproject/luarocks,keplerproject/luarocks,tarantool/luarocks,keplerproject/luarocks