How to attach a JS library to page or block with #attached? I have seen something like the following document for forms:

$form['myelement']['#attached']['libraries_load'][] = array('myAwesomeLibrary');


However, this does not work in render arrays for pages or blocks.  At least, not in Drupal 7. When attaching a JS library to a render array in a page or block, should I use the 'libraries_load' or 'library' key within the '#attached' array?  Neither seem to work.  

Of course, it's possible to use the 'js' key along with libraries_get_path, but I'm not sure that's best practice for Drupal 7, and it doesn't really take advantage of the path in hook_libraries_info.
This might be a simple case of misunderstanding. The difference between libraries_load and library #attached keys can be confusing. 

['#attached']['libraries_load'] is for libraries defined through hook_libraries_info which is in turn a part of the Libraries API module. If a module has defined a hook hook_libraries_info but your installation doesn't have the Libraries API module installed, then that library will never load. The libraries_load key of #attached will not fire for the same reason. Ideally though, this module with the hook_libraries_info should have a dependency on the Libraries API module if it was written correctly.

['#attached']['library'] is for libraries defined through drupal core library api hook_library. This should always work without any additional modules, provided you've defined a hook_library in your module (and not hook_libraries_info)

Hope this helps you get a clearer idea of what's exactly wrong. You can't have these interchanging, and just trying libraries_load or library randomly to see if they work. Both require a certain prerequisite (see above) to function correctly.