Port back recover related changes from twitter's branch

[hellostreaming]

In Distributedlog(apache/distributedlog#150), we temp comment out RecoverCommand in tools/DistributedLogTool.java, because the needed support is not ready here.
We may need to do the porting work from twitter's branch during 4.6.0.

[eolivelli]

Is this an umbrella issue or it is just for a single port of code?

[sijie]

This is an umbrella issue.

[ivankelly]

@sijie @zhaijack are these the autorecovery changes that need to come in from the twitter branch (honouring placement policy etc)? Can we uncomment RecoverCommand now?