Fix #794 unit test should cover changelog to changelog communications

This does not allow to cover the code that deals with changelog server to
changelog server communications.

In order to have more than one changelog services running in the same instance
and instance layout, the serverID has been added to the changelogstate dbName.

Changelog db path is now configurable, 

The 2 following tests have been implemented:

+  /**
+   * Chaining tests of the changelog code with 2 changelog servers involved
+   * 2 tests are done here (itest=0 or itest=1)
+   * 
+   * Test 1
+   * - Create changelog server 1
+   * - Create changelog server 2 connected with changelog server 1
+   * - Create and connect client 1 to changelog server 1
+   * - Create and connect client 2 to changelog server 2
+   * - Make client1 publish changes
+   * - Check that client 2 receives the changes published by client 1
+   * 
+   * Test 2
+   * - Create changelog server 1
+   * - Create and connect client1 to changelog server 1
+   * - Make client1 publish changes
+   * - Create changelog server 2 connected with changelog server 1
+   * - Create and connect client 2 to changelog server 2
+   * - Check that client 2 receives the changes published by client 1
+   * 
+   */