rest/test.py: expect_nofail() to allow examination of reason

Also remove unused MyException

Signed-off-by: Dan Mick <dan.mick@inktank.com>
rest/test.py: retry mds setmap in case epoch has changed

Loop 10 times retrying mds dump/getmap/setmap.

Fixes: #5815
Signed-off-by: Dan Mick <dan.mick@inktank.com>
mon/MDSMonitor: don't call all EINVALs "unrecognized command"

Some of them are valid EINVALs (like mds setmap with the wrong epochnum)

Signed-off-by: Dan Mick <dan.mick@inktank.com>
Merge branch 'wip-5815' into next

Reviewed-by: Sage Weil <sage@inktank.com>