Improve test timing

[relu91]

I did some improvements in our test suites hoping to reduce wasted time while developing with node-wot. With the reference to #831, the situation is improved but it is not perfect. Some caveats:

• fake timers do not work with sockets ( I went deep down inside node.js internals and I figured out that they are not using the usual setTimeout or equivalent method but rather an internal version. Mocking the Socket.setTimeout method does not work either -> I gave up). This still causes some slowness in the Modbus protocol binding.
• mbus still times out at 2sec even if you set another timeout
• OPC-UA is still quite slow.

In general I think we should save about 5 seconds or more each run.

[danielpeintner]

Even small improvements are good improvements 👍

I noticed that there are 2 check warnings about

• sleep no longer used
• counter assigned but value never used

I think we should fix them before merging.