Moves negative tests from api/compute/servers/test_virtual_interfaces

This change set moves the negative tests in test_virtual_interfaces to
a new file test_virtual_interfaces_negative

Also changes line # 43, rand_name(#$%*&^%) to uuid4() to get the invalid
server ID in negative file and 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: Ia6b4c927112318b5b6b4583511537d1cbe020f56
Merge "Moves negative tests from api/compute/servers/test_virtual_interfaces"