Add the remaining DRBD dynamic sync disk params

Add the c-plan-ahead, c-fill-target, c-delay-target, c-max-rate,
c-min-rate parameters; report errors while setting the
synchronization speed.

Change the error signaling model of SetSyncParams. Instead of returning
True or False, return a list of errors (to make possible error reporting
during the recursive call).

Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>