casadm: Don't print invalid info about switch modes during flush

[mmichal10]

Problem:
Currently during flush casadm -L always prints info about switching from wb to current cache mode. It does it during stopping cache or standalone flush. If the current cache mode is WB, casadm prints wb->wb.

Enhancement:
Get rid of the info about switching policies from casadm. Print only the current cache mode and extend the status info to e.g. "Running (Flushing 58.0%)"
For casadm -Q command extend the flushing status with an info about the old and the new cache mode