CHANGE: Rename product_* config options to release_* for consistency with productmd.
ACTION: Rename product_name, product_short, product_version, product_is_layered to release_* in config files.
Rename //variant/product to //variant/release in variants XML.
rename the pungi binary to pungi-koji since it does is tasks in koji
rename pungi-gather to pungi as it is the standalone old pungi binary
there is scripts that expect pungi to be the old pungi, the new binary
is not yet in use, pungi-koji semes to make sense, open to better ideas
