As we move to multiple config backends like local disk and etcd,
config file should not be read from the disk, instead the quick
package should load and verify for duplicate entries.
* Update the GetConfig admin API to use the latest version of
configuration, along with fixes to the corresponding RPCs.
* Remove mutex inside the configuration struct, and inside
notification struct.
* Use global config mutex where needed.
* Add `serverConfig.ConfigDiff()` that provides a more granular diff
of what is different between two configurations.
This change introduces following simplified steps to follow
during config migration.
```
// Steps to move from version N to version N+1
// 1. Add new struct serverConfigVN+1 in config-versions.go
// 2. Set configCurrentVersion to "N+1"
// 3. Set serverConfigCurrent to serverConfigVN+1
// 4. Add new migration function (ex. func migrateVNToVN+1()) in config-migrate.go
// 5. Call migrateVNToVN+1() from migrateConfig() in config-migrate.go
// 6. Make changes in config-current_test.go for any test change
```
