Make the test runs configurable

I use the testnet box https://github.com/freewil/bitcoin-testnet-box to
run my tests. With this patch I can pick which config file to use, and
if I want to test the connect_to_local function.

Specifying the file itself would also allow to run the tests against
various altcoins.
Add --noremote option
Merge pull request #41 from nkuttler/tests_configurable

Make the test runs configurable