Adapted p2p-versionbits-warning.py test to new "unknown version" detection logic
Adapted p2p-versionbits-warning.py test to new "unknown version" detection logic

p2p-versionbits-warning needed a little adaptation after the unknown bit signaling and unknown version detection logic in main.cpp was changed.
The issuance of the "unknown version" warning has changed based on two things:
1. the threshold / window for assessing unknown bits is now 50 / 100, fixed for all networks
2. unconfigured ("unknown") bits are not assessed based on state (this is impossible since we do not know when they activate), but purely on whether they cross the 50% threshold

Some cleanup has also been performed in the file (getting rid of some hardcoded constants in favor of VB_PERIOD, VB_THRESHOLD).

Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,BitcoinUnlimited/BitcoinUnlimited,Justaphf/BitcoinUnlimited