Fixed pipeline parsing and implemented SubPipeline reuse

[AlanAboudib]

Description

Pipeline parsing into subpipelines was not functional when pipe components had different permissions. This is fixed now.

Also, when a pipeline is parsed for multiple data owners, this could result in identical subpipelines among different data owner, in order to reduce redundancy, I implemented subpipeline reuse.

How has this been tested?

• Tested are needed (see issue #177)

I hadn't implemented unit tests yet. Merging this PR is urgent for #pricon2020

Checklist

• [x] I have followed the Contribution Guidelines and Code of Conduct
• [x] I have commented my code following the OpenMined Styleguide
• [x] I have labeled this PR with the relevant Type labels
• [ ] My changes are covered by tests

[Nilanshrajput]

Oh already merged, will check on this changes on the next pr