dist/redhat: Fix baseurl of 3rdparty repo
dist/redhat: Fix baseurl of 3rdparty repo

$basearch isn't parsed as expected, the finaly baseurl is wrong.
We only have x86_64 arch in external 3rdparty repository, and
the conf file is only for x86_64, so it's fine to use hardcode
x86_64.

The problem was introduced by commit
b5e83ebd9432269984cf0ceb758bb21b3abfa0ac ("dist/redhat: switch 3rdparty
packages to external build service").

Fixes #2930

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>
Message-Id: <708f46a7c36623e86fee278462c80db1eff3b820.1509700430.git.eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>

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