Stop an apparent test-network hang when used with make -j2

If (GNU) Make 3.81 is running processes in parallel using -j2 (or more),
it waits until all descendent processes have exited before it returns to
the shell.

When a command like "make -j2 test-network" is run, this means that
test-network.sh apparently hangs until it either make is forcibly
terminated, or all the chutney-launched tor processes have exited.

A workaround is to use make without -j, or make -j1 if there is an
existing alias to "make -jn" in the shell.

We resolve this bug in tor by using "chutney stop" after "chutney verify"
in test-network.sh.
Merge branch 'test-network-hang-on-make-j2'