lib: allow contact points to be a csv

if passed via env var, it won't be an array, but likely a csv.
The driver will accept

- [<host>]
- <host>,<host>
- <host>

semver: patch

lib/index.js

@@ -82,12 +82,13 @@ ScyllaDown.prototype._open = function _open(opts = {}, cb) {
   , replicas = 1
   } = opts
 
-  debug('contact points: ', contactPoints)
+  const hosts = toArray(contactPoints)
+  debug('contact points: ', hosts)
   debug('keyspace', keyspace)
   debug('replicas', replicas)
 
   this.client = new Client({
-    contactPoints: contactPoints
+    contactPoints: hosts
   })
 
   this.keyspace = keyspace
@@ -243,6 +244,12 @@ ScyllaDown.prototype._table = function _table(cb) {
   this.client.execute(query, cb)
 }
 
+function toArray(item) {
+  if (!item) return []
+  if (Array.isArray(item)) return item
+  return typeof item === 'string' ? item.split(CSV_SEP) : [item]
+}
+
 /**
  * Represents a single operations inside of a batch
  * @typedef {Object} Operation