Add check for snapshot to Brick LVM.
Add check for snapshot to Brick LVM.

Adds a check to the LVM code in brick to see if
a snapshot exists.  This implements the incorrectly
named "is_busy" method that exists in the cinder LVM driver.

Change-Id: Ia0f6cbd3d5b4561c5368545448abaafa67caf05d

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