dist/debian: follow renaming of gcc-7.2 packages on Debian 8
dist/debian: follow renaming of gcc-7.2 packages on Debian 8

Now we applied our scylla-$(pkg)$(ver) style package naming on gcc-7.2,
so switch to it.

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <1515522920-8266-1-git-send-email-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

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