WL#1093: Add possibility to read logs from the disk instead of slave

Affects: Server-7.1   —   Status: Un-Assigned   —   Priority: Medium

We shall add possibility for replication to read the logs directly from file
system instead of asking them from the Master.

The main reason for this is automatic log forward recovery from backup+logs, on
server level instead of using external tool, which is hard to keep in sync

The next reason is - this would allow to setup "shared disk" based replication,
which has its own benefits:

  -Distributed file system takes care of log files distribution over network
caching etc automatically. This removes master as bottleneck and allows to use
ore simple setup with large amount of slave
  -In case of master crash recovery is simplified as all slaves are still in sync 
   with each other.
  -Fallback implementation is more trivial - you can just broughtup new master
which will continue writing logs to the same location without hassle with slaves
positions resync.