Remove usage of getFileVersionQuorumMap, instead use listFileVersions
to get the version list and extract higherVersion.
Fixes#1379Fixes#1378Fixes#1377
* xl/selfheal: selfheal based on read quorum on GET
* xl: getReadableDisks() also returns whether self-heal is needed so that this info can be used by ReadFile/SelfHeal/StatFile.
* xl: trigger selfheal from StatFile.