Refactor api.catalog.search() method to provide 'next_marker' value

That way it works like Glance (see http://tinyurl.com/jwqtj23) and
allows for complex query pagination (to cycle through pages filtered
by some criteria, muranoclient uses 'next_marker' pointer).

Implements: blueprint app-catalog-pagination
Change-Id: If71da70fa835a1ee7a271ebf7238c0a4c64d4123
Merge "Refactor api.catalog.search() method to provide 'next_marker' value"