function wrapCommand( cmd ) {
	return [
		'"async";',
		'(function __iife__() {',
		'function __onResult__(result) {__done__(null, result);};',
		'function __onError__(error) {__done__(error);};',
		'var __p__ = '+cmd+';',
		'__p__.then(__onResult__, __onError__);',
		'})()'
	].join( '' );
}
Wraps an `async`/`await` command string in order to handle the result of the returned promise.

@private
@param {string} cmd - command to wrap
@returns {string} wrapped command