Fix hook documentation on entry_points config

The syntax suggested for adding hooks to nova via setup.py entrypoints is:

    entry_points = {
        'nova.hooks': [
            'resize_hook': your_package.hooks.YourHookClass,
        ]
    },

But this is incorrect. The proper syntax for an entry_points entry is:

    entry_points = {
        'nova.hooks': [
            'resize_hook=your_package.hooks:YourHookClass',
        ]
    },

Change-Id: Id7bc6891dc542d4317e82e15300c7293eb0d17a0
Closes-bug: #1374666
Merge "Fix hook documentation on entry_points config"