node: Add a function to wait for apt not to run
node: Add a function to wait for apt not to run

At cassandra node startup apt command will run
in the background. SCT must wait them to have
finished their work before being able to proceed.

Add node.wait_apt_not_running() and deploy it.

Signed-off-by: Benoît Canet <ecd1f14f7c1c6dc7a40210bdcc3810e0107ecbc8@scylladb.com>

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