New --release option
Introduce a new global option --release to represent what --dist does. This is
a replacement, --dist will be disabled eventually after a while.
Original --dist is used to overwrite the name got from remote branch, and then
determine the build target and dist macro to build RPM. Where the name is
actually the release name, e.g. f24 and f25. Hence, --release could be much
clear and easier for users to know what behavior it will affect.
Signed-off-by: Chenxiong Qi <cqi@redhat.com>