List all tenant images/snapshots on admin images view

Admin's Images panel shows only instance snapshots of the project
selected on Projects tab .
Add the appropiate filter is_public: None to the list request.

Change-Id: I4963515d8dbdc89512258c30e3fad309f9720436
Closes-Bug: #1283258
sort flavors on Resize Instance modal

in the new flavor dropdown menu, it is sorted by id right now,
changed so that it matches that in create instance, sorted
 by ascending RAM usage

I refactored out the common flavor sorting code into instances/util.py
that is shared by create_instance and resize_instance

Change-Id: I40dedcf87dbcfb7128185445510d9ec96462abb2
Closes-Bug: #1279135
Merge "sort flavors on Resize Instance modal"
Merge "List all tenant images/snapshots on admin images view"