Migration sql changes (#199)

* safe migration script changes

* lamassu migration script fixes

migrations/032-create_machine_pings_table.js

@@ -2,24 +2,24 @@ var db = require('./db')
 
 exports.up = function (next) {
   var sql = [
-    `create table machine_pings (
-    id uuid PRIMARY KEY,
-    device_id text not null,
-    serial_number integer not null,
-    device_time timestamptz not null,
-    created timestamptz not null default now())`,
-    `create table aggregated_machine_pings (
-    id uuid PRIMARY KEY,
-    device_id text not null,
-    dropped_pings integer not null,
-    total_pings integer not null,
-    lag_sd_ms integer not null,
-    lag_min_ms integer not null,
-    lag_max_ms integer not null,
-    lag_median_ms integer not null,
-    day date not null)`,
-    'alter table machine_events drop column device_time',
-    'alter table machine_events add column device_time timestamptz'
+    `create table if not exists machine_pings (
+      id uuid PRIMARY KEY,
+      device_id text not null,
+      serial_number integer not null,
+      device_time timestamptz not null,
+      created timestamptz not null default now())`,
+    `create table if not exists aggregated_machine_pings (
+      id uuid PRIMARY KEY,
+      device_id text not null,
+      dropped_pings integer not null,
+      total_pings integer not null,
+      lag_sd_ms integer not null,
+      lag_min_ms integer not null,
+      lag_max_ms integer not null,
+      lag_median_ms integer not null,
+      day date not null)`,
+    db.dropColumn('machine_events', 'device_time'),
+    db.addColumn('machine_events', 'device_time', 'timestamptz')
   ]
   db.multi(sql, next)
 }