Integrating Scriber into Corgie

[supersergiy]

Integrating the basic version of scriber into corgie and mazepa.

Verified to produce correct results with NormalizationJob and AlignBlockJob.

MergeRender tasks shrunk to 2KB

To test: use mazepa -e git+https://github.com/supersergiy/scheduler.git@8905783b680cafcebfec52fec7f0e68e4be0e5fd#egg=mazepa`

[nkemnitz]

• objectscriber needs to be added to the requirements
• This line in MiplessCloudVolume.__init__ is problematic:

  corgie/corgie/mipless_cloudvolume.py

  Lines 91 to 92 in d6a973a

  	if 'info' in self.cv_params and overwrite:
  	self.store_info()

  Only the scheduler should create/overwrite the info file - right now all workers will try to rewrite the info file simultaneously, which is causing e.g. GCS to panic with 429 errors.

Is there a good way to figure out if the job was initialized by the worker or the scheduler?

[nkemnitz]

• DownsamplingJob workers suddenly complained about the dst_layer (not specified) being readonly

[supersergiy]

Thanks for the feedback! I'll address these issues asap

[supersergiy]

Added a global settings.py file which keeps track of whether the process is worker or not. Workers don't upload info.
Added objectscriber to setup.py.
Solved the downsample issues.
@nkemnitz

[nkemnitz]

Just one typo - see suggestion
Besides objectscriber, does this PR also require a minimal mazepa version? If so, that should be specified.