When an account is switched to interest-only mode due to no interest,
it was not possible to switch that account more than once. But the
function switchAccountToInterestMode() that triggers a switch could
possibly doing it more than once. This should not cause problems
but increased the number of traces in a big super cluster.
Also fixed some flappers and a data race.
Signed-off-by: Ivan Kozlovic <ivan@synadia.com>