Remove duplicate negative test of flavor_id

As tempest/api/compute/admin/test_flavors.py, it is possible to
specify uuid as flavor_id. In addition, Nova creates a flavor with
uuid flavor_id if passing None as the API parameter of flavor_id.

Then, test_get_flavor_details_for_invalid_flavor_id is not an
"invalid id" test, the test is a "non existent id" test.
So the test and test_non_existent_flavor_id are duplicated, and
this patch merges them to one test.

Change-Id: I73f79f82f48a49208500c2542e55c026f120e921
Separate negative tests for test_availability_zone

Move negative tests from test_availability_zone.py to
test_availability_zone_negative.py

This patch also uses 'AZ' short for the 'AvailabilityZone'.
This is because if the class name 'AvailabilityZoneAdminV3
NegativeTestJSON' is used, the tempest test will occur an
error 'Project name should not be greater than 64 characters.'
The Project name is made of class name and the characters
'-tempest-xxxxxxxxxx-tenant'.
'-tempest-xxxxxxxxxx-tenant' is 26 characters, so the class
name should not exceed 38 characters.

Partially implements blueprint negative-test-files
Change-Id: Ic72264e89ac5fd700202b0c75cc63116d8fca172
Merge "Separate negative tests for test_availability_zone"
Merge "Remove duplicate negative test of flavor_id"