skip overlimit tests when default quota set is -1
skip overlimit tests when default quota set is -1

testcase <test_resize_server_using_overlimit_ram> is intended to create
flavor using overlimit ram, but if the tenant's default ram quota set
is -1, we will get "ERROR (BadRequest): Quota limit 0 for cores must be
greater than or equal to already used and reserved 1. (HTTP 400)" when
creating flavor with ram=0(-1 + 1 = 0).

so testcase <test_resize_server_using_overlimit_ram> should be skipped
if default quota set is -1

<test_resize_server_using_overlimit_vcpus> is the same.

Change-Id: Ia823b4b0170119cd8f17c72e6eabae0a4a042c9e
Closes-Bug: #1540780

openstack/tempest,Tesora/tesora-tempest,zsoltdudas/lis-tempest,cisco-openstack/tempest,Juniper/tempest,LIS/lis-tempest,vedujoshi/tempest,masayukig/tempest,cisco-openstack/tempest,sebrandon1/tempest,masayukig/tempest,openstack/tempest,vedujoshi/tempest,bigswitch/tempest,sebrandon1/tempest,zsoltdudas/lis-tempest,Tesora/tesora-tempest,LIS/lis-tempest,Juniper/tempest,bigswitch/tempest