refactor into docker.update

src/docker.js

@@ -29,7 +29,8 @@ exports = module.exports = {
     memoryUsage,
     createVolume,
     removeVolume,
-    clearVolume
+    clearVolume,
+    update
 };
 
 var addons = require('./addons.js'),
@@ -699,3 +700,17 @@ function info(callback) {
         callback(null, result);
     });
 }
+
+function update(name, memory, memorySwap, callback) {
+    assert.strictEqual(typeof name, 'string');
+    assert.strictEqual(typeof memory, 'number');
+    assert.strictEqual(typeof memorySwap, 'number');
+    assert.strictEqual(typeof callback, 'function');
+
+    const args = `update --memory ${memory} --memory-swap ${memorySwap} ${name}`.split(' ');
+    // scale back db containers, if possible. this is retried because updating memory constraints can fail
+    // with failed to write to memory.memsw.limit_in_bytes: write /sys/fs/cgroup/memory/docker/xx/memory.memsw.limit_in_bytes: device or resource busy
+    async.retry({ times: 10, interval: 60 * 1000 }, function (retryCallback) {
+        shell.spawn(`update(${name})`, '/usr/bin/docker', args, { }, retryCallback);
+    }, callback);
+}