update: reset flags before and after each osd node upgrade

update: reset flags before and after each osd node upgrade

It might be possible at some point even with osd flags `noout` and
`norebalance` set the PGs states can change depending on the amount of data
written meantime. It means the check for PGs state will fail.

This commit changes the way we set those flags:
we set them before an OSD node upgrade and unset them before the PGs
state check so they can recover.

Fixes: #3961
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>