Rename duplicated class name AttachVolumeMultiAttachTest

Class name AttachVolumeMultiAttachTest is duplicated in
api.compute.admin.test_volume_swap.py and
api.compute.volumes.test_attach_volume.py, which is not
good for code readability, so this is to rename
test_volume_swap.AttachVolumeMultiAttachTest
to a more suitable name "TestMultiAttachVolumeSwap".

Change-Id: I079d54a6bf05dc4ce3a217236b6f7c42470bc479
1 file changed