The following tempest test is failing regularly in the gate:
tempest.api.compute.volumes.test_attach_volume.AttachVolumeTestJSON.test_list_get_volume_attachments
The theory behind this fix is that tests are creating/deleting /dev/sdX
devices and LVM ends up attempting to open an already removed device which
causes LVM to temporarily block. Setting the global_filter will limit the
block devices that are used by LVM system components.
This adds a new config option config.cinder.loop-device. In not set the
loop device will be generated.
Closes-Bug: #1918306
Change-Id: I8cccf7a1b1af2e15106b11023652af23c7715e6f