Replace os.unlink with delete_if_exists
Replace os.unlink with delete_if_exists

Shouldn't care when doing unlink on our temp files
if they exist or not.  In fact this causes problems
when you do things like with tempfile/dir and happen
to try and unlink after it's already been removed.

This replaces these calls with the safer
common.fileutils.delete_if_exists which will
ignore the os exception of the object DNE.

Fixes bug: 1212502

Change-Id: Ica86c95f736411da486335aec5512e59247bfbc0

sasukeh/cinder,Hybrid-Cloud/cinder,nikesh-mahalka/cinder,j-griffith/cinder,cloudbau/cinder,Akrog/cinder,abusse/cinder,Thingee/cinder,nikesh-mahalka/cinder,tlakshman26/cinder-new-branch,takeshineshiro/cinder,hguemar/cinder,cloudbase/cinder,JioCloud/cinder,apporc/cinder,takeshineshiro/cinder,JioCloud/cinder,manojhirway/ExistingImagesOnNFS,apporc/cinder,Datera/cinder,Paul-Ezell/cinder-1,rickerc/cinder_audit,alex8866/cinder,leilihh/cinder,ntt-sic/cinder,Thingee/cinder,mahak/cinder,bswartz/cinder,Nexenta/cinder,scottdangelo/RemoveVolumeMangerLocks,potsmaster/cinder,nexusriot/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,blueboxgroup/cinder,petrutlucian94/cinder,Datera/cinder,abusse/cinder,julianwang/cinder,duhzecca/cinder,NeCTAR-RC/cinder,eharney/cinder,tlakshman26/cinder-new-branch,dims/cinder,hguemar/cinder,alex8866/cinder,CloudServer/cinder,leilihh/cinder,NetApp/cinder,Akrog/cinder,Hybrid-Cloud/cinder,ntt-sic/cinder,tlakshman26/cinder-https-changes,spring-week-topos/cinder-week,sasukeh/cinder,scottdangelo/RemoveVolumeMangerLocks,Paul-Ezell/cinder-1,phenoxim/cinder,ge0rgi/cinder,phenoxim/cinder,redhat-openstack/cinder,potsmaster/cinder,NetApp/cinder,github-borat/cinder,Nexenta/cinder,github-borat/cinder,rickerc/cinder_audit,cloudbau/cinder,eharney/cinder,Accelerite/cinder,tlakshman26/cinder-bug-fix-volume-conversion-full,Accelerite/cinder,spring-week-topos/cinder-week,petrutlucian94/cinder,duhzecca/cinder,bswartz/cinder,manojhirway/ExistingImagesOnNFS,cloudbase/cinder,NeCTAR-RC/cinder,mahak/cinder,blueboxgroup/cinder,j-griffith/cinder,redhat-openstack/cinder,rakeshmi/cinder,dims/cinder,julianwang/cinder,winndows/cinder,openstack/cinder,tlakshman26/cinder-https-changes,saeki-masaki/cinder,saeki-masaki/cinder,rakeshmi/cinder,winndows/cinder,scality/cinder,openstack/cinder,scality/cinder,nexusriot/cinder,CloudServer/cinder,Thingee/cinder