fix(option parse): fix a typo in choise list of --dist-version
fix(option parse): fix a typo in choise list of --dist-version

Lack of a comma after 'focal', then 'focal' and 'jessie' are connected
unexpectedly.

Error: Invalid value for "-v" / "--dist-version": invalid choice: focal.
       (choose from xenial, trusty, bionic, focaljessie, stretch, buster)

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>

scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests