Do not assume order of images

This fixes the test_tag_lifecycle test, which broke with a randomized
PYTHONHASHSEED.

Previously, the test assumed that the values in the list of tag names
would remain constant. The test now sorts the results and compares to a
sorted set.

Change-Id: If5a2ef683fcf55520c7d539f1b90aefaba4739d5
Partial-bug: #1348818
Merge "Do not assume order of images"