- Add Exception communication from server to client

Iteration 2: Disk Quota

- Random function that generates  QuotaException. For testing end to end
  exception flow. Later this will be replaced by appropriate quota
  checks

Iteration 3: Disk Quota

- compute the bytes written to index and data files in each reducer. Add
  this information to the filename
- estimate the total disk size in bytes needed for a <node, store> pair.
  Done by iterating through all the index and data files and getting
  theie sizes from the file names, after the job is run.

Iteration 4: Disk Quota

- In HDFSFetcher, fetch estimated disk size from metadata file
- In HDFSFetcher, fetch disk quota limit for <node, store> pair using admin client

Minor fix: Add log message

Minor fix: Fix exception handling

minor fix: Handle Quota Exceptions appropriately

minor fix: Fix more exceptions

More fixes for Exception logs

More exception handling fixes

Handling Quota Exception in AdminStoreSwapper

Iteration 5: Fix disk estimation logic

- Instead of renaing the .data and .index files, add the file size info to corresponding '.checksum' files
- Introduce new CheckSumMetadata file that holds the following fields - checksum, data file size, index file size
- CheckSumMetadata is similar to ReadOnlyStorageMetadata file in terms of serialization and deserialization

minor fix: exclude unnecessary "_" in file names

Cleanup debug logs

Add quota checks

- Determine if quota needs to be checked for the incoming push. For pre
  existing stores quota is not checked. They will be quota-ed in future.
- Check if there is sufficient quota left for a new push.
- Filter out stores that push data mistakenly to the Voldemort cluster.
  This is based on the assumption that for invalid stores, during build
  phase, a store definition is with 0 quota. All other stores that are
  onboarded through Nuage will have proper quota set already.

More fixes:

- Fix Non Quota Exception Handling.  Propogates actual error message to client
  side.
- Change getQuota() to getQuotaForNode() in HDFSFetcher.
- Add debug log messages
- Set zero Quota for stores that are created during Build and Push. We
  want all new stores to be pre created with appropriate quota via Nuage
  or via admin client.