test: fix nock usage

by default, nock intercepts and redirects everything to 127.0.0.1:80
this is regardless of any http request is mocked or not

nock.isActive() - is interceptor active
nock.restore() removes the interceptor
nock.activate() - enables interceptor again

nock.cleanAll() - deletes all mocks. nothing to do with interceptor
nock.activeMock() - to get the active mocks
nock.persist(true/false) - the mock will reply once and set isDone(). but you can persist(true)

src/test/system-test.js

@@ -8,12 +8,16 @@
 
 const common = require('./common.js'),
     expect = require('expect.js'),
+    nock = require('nock'),
     system = require('../system.js');
 
 describe('System', function () {
     const { setup, cleanup } = common;
 
-    before(setup);
+    before(async function () {
+        await setup();
+        if (nock.isActive()) nock.restore(); // required to connect to the docker socket
+    });
     after(cleanup);
 
     it('can get filesystems', async function () {