Do not flush the cache after every block outside of IBD
Set -discover=0 in regtest framework

The regtest framework is local, so often there is no need to
discover our external IP.  Setting -discover=0 in util.py works
around shutdown hang caused by GetExternalIP waiting in recv().
Use unordered_map for CCoinsViewCache with salted hash
Merge pull request #4494

bc42503 Use unordered_map for CCoinsViewCache with salted hash (Pieter Wuille)
Merge pull request #4505

d4d3fbd Do not flush the cache after every block outside of IBD (Pieter Wuille)
Add peerid to getpeerinfo to allow correlation with the logs.

This seems to have been missed in 3764.
Merge pull request #4522 from dgenr8/set_discover_0

Set -discover=0 in regtest framework
Merge pull request #4535

c4a321f Add peerid to getpeerinfo to allow correlation with the logs. (Gregory Maxwell)
Allow the node to run on a pruned state
Check for missing undo files at startup, making the check somewhat more efficient.