Plugin Broker doesn't work on multi-user Che

[sleshchenko]

Description

Plugin Broker doesn't work on multi-user Che.
The error that I faced during starting workspace with configured plugins - Plugin Broker failed to start because it didn't specify machine token while connecting to Che Server.
The scope of this issue is making Plugin Broker working on multi-user Che by using machine token and other possible issues which may occur on further phases of plugin broking.

Reproduction Steps

1. Deploy Che with Plugin Registry configured.
2. Create a workspace with configured plugins.
3. Try to start the workspace.
   Expected: Workspace is started.
   Actual: Workspace is failed because of timeout
   Actually, Plugin Broker failed because of Che Server connection establishing error.