Unit test fails in pbuilder environment
Unit test fails in pbuilder environment

When running tests inside a pbuilder environment we don't
have /dev/disk/by-path directory and so the test_host_driver
test fails. Fix test by overriding the isdir method to
return True and pretend that the directory is there.

Change-Id: Ifd39d796b7f250b1ec45227a4262ebb33d5656bf

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