Moves negative tests from api/compute/keypairs/test_keypairs

This change set seperates negative tests in test_keypairs to a
new negative file test_keypairs_negative.

Note: HACKING.rst
The second requirement is that all negative tests must be added to a negative
test file. If such a file doesn't exist for the particular resource being
tested a new test file should be added

Change-Id: I18f195d8470e6a9a135ee346a3489ba5d553b0a1
Merge "Moves negative tests from api/compute/keypairs/test_keypairs"