Concurrency test issues for 7.7 release - round 2

Concurrency testing continued for about 20 minutes. Core functionality was not working fine though it was slow.

Issues
1. All the request was diverted to single node by load balancer, improve the README.txt for the load balancer setup
2. Exceptions are still seen in CMS dashboard when any document / image / asset is copied /moved (HGGE-16)
3. "No server is available to handle this request" and "503 error" occurred three times, after a minute of so it was working fine again

Good things
1. Channel manager was working fine when two persons were working on different channels
2. Restarting the nodes with same repository did not throw any error after concurrency test