New drupalModuleInstall nightwatch command

To facilitate enabling modules during nightwatch tests a new drupalModuleInstall command has been added.

Usage:

The command accepts a single string as parameter which is the machine name of the module to enable. This command does not handle enabling a module with dependencies (dependencies should be enabled first, also via a call to drupalModuleInstall). The command does not handle enabling experimental or obsolete modules. More generally, any module enabling that requires a confirmation step is not supported by this command.

// core/modules/toolbar/tests/src/Nightwatch/Tests/toolbarTest.js
module.exports = {
  '@tags': ['core'],

  before(browser) {
    browser
      .drupalInstall()
      // The breakpoint module is a dependency of toolbar, enable it first.
      .drupalInstallModule('breakpoint')
      .drupalInstallModule('toolbar');
  },
};