Adds 3 additional tests to test_flavor.py script

Adds three additional scenarios to flavor-manage functionality.
The test cases are added to the script test_flavors.py present in
"/tempest/tempest/tests/compute/admin" folder. Also adds try and
finally blocks to the already existing test cases.
Modified the "create_flavor" method in flavors_client.py and
made extra data as optional paramters instead of mandatory ones.

Change-Id: I8791dfc0cf1df6c1788b5c7e05f99e6eda989823
Implements: blueprint add-tests-flavor-manage
3 files changed