fa2cdc9ac2 test: Simplify create_cache (MarcoFalke)
fa25210d62 qa: Fix wallet_txn_doublespend issue (MarcoFalke)
1111aecbb5 qa: Always refresh stale cache to be out of ibd (MarcoFalke)
fab0d85802 qa: Remove mocktime unless required (MarcoFalke)
Pull request description:
When starting a test, we are always in IBD because the timestamps on cached blocks are in the past. Usually, we solve that by generating a block at the beginning of the test.
That is clumsy and might even lead to other problems such as #15360 and https://github.com/bitcoin/bitcoin/issues/14446#issuecomment-461926598
So fix that by getting rid of mocktime and always refreshing the last block of the cache when starting the test framework.
Should fix#14446
Tree-SHA512: 6af09800f9c86131349a103af617a54551f5f3f3260d38e14e3f30fdd3d91a0feb0100c56cbb12eae4aeac5571ae4b530b16345cbb831d2670237b53351a22c1