Add test for wallet password race
Add test for wallet password race

When the wallet password is modified it currently is a non-atomic operation.

While we consider how to change the design to mitigate the condition, here's a test case that reproduces the problem.
clemahieu/raiblocks,clemahieu/raiblocks,clemahieu/raiblocks,clemahieu/raiblocks,SergiySW/raiblocks,clemahieu/raiblocks,clemahieu/raiblocks,SergiySW/raiblocks,SergiySW/raiblocks,SergiySW/raiblocks,SergiySW/raiblocks