make retry time a multiple of the expected block time
make retry time a multiple of the expected block time

Previously thet were the same and causes a race condition.  If the
miner time was fractionally larger than the expected time then a
timeout would occur.  This could occur multiple times an case very
long times.

Signed-off-by: Christopher Hall <97c3bc3fef1a71b149f1095f758464e4b18eb35b@bitmark.com>

bitmark-inc/bitmarkd,bitmark-inc/bitmarkd