Improve functional test base for microversion
Improve functional test base for microversion

In current functional tests, when we test some
features base on microversion, we need to define
request_api_version in order to get template/sample,
but when we call the base functions, like: _do_get,
_do_post, _do_put, _do_delete, we must pass the argument
'api_version' to specify X-OpenStack-Nova-API-Version,
even if we had defined request_api_version in test class.
Do refactor, make request_api_version as default value
when 'api_version' is None so that the functional tests are
more readable.

Change-Id: I6163cb18b82ffa80ccde23f7f555e253bfec78b0

openstack/nova,rahulunair/nova,j-carpentier/nova,mahak/nova,Juniper/nova,scripnichenko/nova,j-carpentier/nova,mahak/nova,klmitch/nova,barnsnake351/nova,bigswitch/nova,TwinkleChawla/nova,noironetworks/nova,Juniper/nova,klmitch/nova,hanlind/nova,hanlind/nova,CCI-MOC/nova,cernops/nova,rajalokan/nova,CEG-FYP-OpenStack/scheduler,fnordahl/nova,nikesh-mahalka/nova,alaski/nova,felixma/nova,noironetworks/nova,gooddata/openstack-nova,cloudbase/nova,openstack/nova,Francis-Liu/animated-broccoli,jianghuaw/nova,mikalstill/nova,rajalokan/nova,rahulunair/nova,vmturbo/nova,cyx1231st/nova,cyx1231st/nova,phenoxim/nova,yosshy/nova,felixma/nova,klmitch/nova,jianghuaw/nova,CCI-MOC/nova,JianyuWang/nova,gooddata/openstack-nova,edulramirez/nova,CEG-FYP-OpenStack/scheduler,apporc/nova,JianyuWang/nova,vmturbo/nova,isyippee/nova,apporc/nova,ted-gould/nova,rahulunair/nova,barnsnake351/nova,whitepages/nova,openstack/nova,MountainWei/nova,jianghuaw/nova,whitepages/nova,MountainWei/nova,mikalstill/nova,NeCTAR-RC/nova,edulramirez/nova,zhimin711/nova,shail2810/nova,BeyondTheClouds/nova,BeyondTheClouds/nova,isyippee/nova,rajalokan/nova,jianghuaw/nova,cloudbase/nova,gooddata/openstack-nova,mahak/nova,vmturbo/nova,zhimin711/nova,shail2810/nova,TwinkleChawla/nova,NeCTAR-RC/nova,devendermishrajio/nova,yosshy/nova,mikalstill/nova,Juniper/nova,cloudbase/nova,gooddata/openstack-nova,bigswitch/nova,fnordahl/nova,nikesh-mahalka/nova,cernops/nova,rajalokan/nova,sebrandon1/nova,raildo/nova,sebrandon1/nova,dims/nova,BeyondTheClouds/nova,Francis-Liu/animated-broccoli,devendermishrajio/nova,hanlind/nova,raildo/nova,dims/nova,klmitch/nova,vmturbo/nova,sebrandon1/nova,cernops/nova,scripnichenko/nova,ted-gould/nova,Juniper/nova,alaski/nova,phenoxim/nova