[tests] skip zapwallettxes.py

[jnewbery]

Temporary fix for #10678

zapwallettxes.py doesn't test anything due to a syntax error.

Fixing the syntax error causes the test to fail because of bad interaction between zapwallettxes and persistent mempool. There is a fix for that in #10330

Until #10330 is merged we should disable this test. There's no point in running a test that doesn't actually test anything, and which occasionally causes spurious Travis failures.

[MarcoFalke]

Tend to NACK. I'd rather have just the fix merged than a total of three pulls. (disable test, fix interaction, enable test)

[TheBlueMatt]

Lets merge #10330!

[jnewbery]

I'd rather have just the fix merged

ok, let's merge it :)