Tests are installed by default

[Flowdalic]

The Tests are installed by default, this triggers an error when packaging electrumx for gentoo via an ebuild. I had to

sed -i "s/find_packages()/find_packages(exclude=('tests',))/" setup.py

Common python packaging practice is to exclude 'tests', 'contrib' and 'docs' from the default installation. For easier packaging of electrumx, not only for gentoo but all distributions, I suggest to exclude 'tests' from being installed as default