tests: update aux raid support

tests: update aux raid support

For raid1  use chunksize as bitmap-chunk specification.
Always enforce usage of bitmap - getting comparable outcome
as lvm2 raid support uses.
Add udev_wait after stopping  md array - as in fact leg-device
are still in use by target even command has finished.

(mdadm --stop causes WATCH rule wakeup, and
ioctl(STOP_ARRAY) returns IMHO to early - it should finish
and fsync work on leg devices first).