bug hunting: attempt to lock coins for Tap addr until 10min time out

[ffranr]

This PR shouldn't be merged.

This PR attempts to reproduce bug: #508

It does so by creating an itest that does the following using the same Tap address throughout:

1. Kick off an asset send event. Do not mine.
2. Kick off another send event. This should through up a coin lock error and force the address to get stuck behind a timeout.
3. Mine 6 blocks.
4. Kick off another send event which should have succeeded (but does not) were it not for step 2.

In it's current state, this PR does not capture the bug. I thought that it used to, but having cleaned up the code, it doesn't anymore.

[Roasbeef]

In it's current state, this PR does not capture the bug. I thought that it used to, but having cleaned up the code, it doesn't anymore.

I thought it was more like:

• send to asset using addr A
• mine a block
• send again using addr A
• it fails oddly

[ffranr]

Closing in favour of #529