'return whether a volume exists'

def exists(self):

    volume_mount_found = False
    volume_found = self.resource.exists_volume(self.volume)
    if ((not self.volume_mount) and volume_found):
        return True
    if self.volume_mount:
        volume_mount_found = self.resource.exists_volume_mount(self.volume_mount)
    if (volume_found and self.volume_mount and volume_mount_found):
        return True
    return False
