configure.py: use {mode} instead of $mode on scylla-package.tar.gz build target
configure.py: use {mode} instead of $mode on scylla-package.tar.gz build target

It's better to use {mode} to extract fixed path just like other build targets do.

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla