Moves negative tests from test_absolute_limits

This change set moves the negative tests in
tempest/api/compute/limits/test_absolute_limits to
a new file test_absolute_limits_negative

Also removes usage of modules directly.

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: Ia331fc4089c773025e192eeef7b0546020d628b8
Merge "Moves negative tests from test_absolute_limits"