Copy utils from cytube-common and remove dep

The `cytube-common` module was created as part of a now-defunct
experiment and since then has just remained a crufty container for a few
utils.  Moved the utils to the main repo and removed the dependency.

src/redis/lualoader.js

@@ -0,0 +1,44 @@
+import fs from 'fs';
+import logger from '../logger';
+
+const CACHE = {};
+const EVALSHA_CACHE = {};
+
+export function loadLuaScript(filename) {
+    if (CACHE.hasOwnProperty(filename)) {
+        return CACHE[filename];
+    }
+
+    CACHE[filename] = fs.readFileSync(filename).toString('utf8');
+    return CACHE[filename];
+}
+
+function loadAndExecuteScript(redisClient, filename, args) {
+    return redisClient.scriptAsync('load', loadLuaScript(filename))
+            .then(sha => {
+        EVALSHA_CACHE[filename] = sha;
+        logger.debug(`Cached ${filename} as ${sha}`);
+        return runEvalSha(redisClient, filename, args);
+    });
+}
+
+function runEvalSha(redisClient, filename, args) {
+    const evalInput = args.slice();
+    evalInput.unshift(EVALSHA_CACHE[filename])
+    return redisClient.evalshaAsync.apply(redisClient, evalInput);
+}
+
+export function runLuaScript(redisClient, filename, args) {
+    if (EVALSHA_CACHE.hasOwnProperty(filename)) {
+        return runEvalSha(redisClient, filename, args).catch(error => {
+            if (error.code === 'NOSCRIPT') {
+                logger.warn(`Got NOSCRIPT error for ${filename}, reloading script`);
+                return loadAndExecuteScript(redisClient, filename, args);
+            } else {
+                throw error;
+            }
+        });
+    } else {
+        return loadAndExecuteScript(redisClient, filename, args);
+    }
+}

src/redis/redisclientprovider.js

@@ -0,0 +1,49 @@
+import clone from 'clone';
+import redis from 'redis';
+import Promise from 'bluebird';
+Promise.promisifyAll(redis.RedisClient.prototype);
+Promise.promisifyAll(redis.Multi.prototype);
+
+/**
+ * Provider for RedisClients.
+ */
+class RedisClientProvider {
+    /**
+     * Create a new RedisClientProvider.
+     *
+     * @param {Object} redisConfig default configuration to use
+     * @see {@link https://www.npmjs.com/package/redis}
+     */
+    constructor(redisConfig) {
+        this.redisConfig = redisConfig;
+    }
+
+    /**
+     * Get a RedisClient.
+     *
+     * @param {Object} options optional override configuration for the RedisClient
+     * @return {RedisClient} redis client using the provided configuration
+     */
+    get(options = {}) {
+        const config = clone(this.redisConfig);
+        for (const key in options) {
+            config[key] = options[key];
+        }
+
+        const client = redis.createClient(config);
+        client.on('error', this._defaultErrorHandler);
+
+        return client;
+    }
+
+    /**
+     * Handle an <code>'error'</code> event from a provided client.
+     *
+     * @param {Error} err error from the client
+     * @private
+     */
+    _defaultErrorHandler(err) {
+    }
+}
+
+export default RedisClientProvider