Improve share snapshots list API filtering

This change adds possibility to filter share snapshots in a lot of possible
ways.
All types of share snapshots listing were updated to support additional
filtering by:
- source share id
- usage (only used by shares, only not used or any)
- limit and offset a la pagination
And sorting by:
- key of models.ShareSnapshot
- direction (asc, desc)

Removed one related CLI test, because it requres existing entities and
absense of them causes error.

Implements blueprint improve-snapshot-list-filtering

Change-Id: Idef60ddc9f54d3b2f0bcb63097bfd1f9072a1df6
Merge "Improve share snapshots list API filtering"