fuzz: add harness for the compact blocks protocol

This harness does one of the following operations in a loop:
- send a cmpctblock message to the test node
- send a blocktxn message to the test node
- send a headers message to the test node
- send a sendcmpct message to the test node
- send a tx message to the test node
- mine a block
- set mock time

The initialize function creates a TestingSetup and mines 200 blocks. Each fuzz
iteration will then create a TestingSetup and copy the cached data directory via
-fuzzcopydatadir.

Author: Crypt-iQ

src/test/fuzz/CMakeLists.txt

@@ -25,6 +25,7 @@ add_executable(fuzz
   chain.cpp
   checkqueue.cpp
   cluster_linearize.cpp
+  cmpctblock.cpp
   coins_view.cpp
   coinscache_sim.cpp
   connman.cpp