feat(config): Allow --user-data-dir to be set in launcher properties

Introduce a new parameter to custom launder properties: `chromeUserDir`
which allows to set the `--user-data-dir` command line option to point
to a specific place. Rationale:
Sometimes it is useful to run Chrome under Karma with certain plugins
loaded. One use-case is to have the **JetBrains IDE Support** plugin to
attach the IntelliJ debugger. We can do it with `--load-extension` but
this can also be prohibited by corporate policy. So one way to solve it
is to have the `--user-data-dir` point to a project subdirectory and to
install the plugin manually on the first run. It is preserved of course
on subsequent runs.

index.js

@@ -21,6 +21,7 @@ var ChromeBrowser = function (baseBrowserDecorator, args) {
   baseBrowserDecorator(this)
 
   var flags = args.flags || []
+  var userDataDir = args.chromeDataDir || this._tempDir
 
   this._getOptions = function (url) {
     // Chrome CLI options
@@ -32,7 +33,7 @@ var ChromeBrowser = function (baseBrowserDecorator, args) {
     })
 
     return [
-      '--user-data-dir=' + this._tempDir,
+      '--user-data-dir=' + userDataDir,
       '--no-default-browser-check',
       '--no-first-run',
       '--disable-default-apps',