Defferable server

[esmakokten]

Summary of this Pull Request (PR)

This PR includes the scheduling policy for deferrable server.
There is no intention to merge it for know, not well tested and still in the process.
I try to comment all the temporary and hacky points.

Thanks!

Intent for your PR

Choose one (Mandatory):

• This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory):

(Specify @<github.com username(s)> of the reviewers. Ex: @user1, @user2)

Code Quality

As part of this pull request, I've considered the following:

Style:

• Comments adhere to the Style Guide (SG)
• Spacing adhere's to the SG
• Naming adhere's to the SG
• All other aspects of the SG are adhered to, or exceptions are justified in this pull request
• I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

Code Craftsmanship:

• I've made an attempt to remove all redundant code
• I've considered ways in which my changes might impact existing code, and cleaned it up
• I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• I've commented appropriately where code is tricky
• I agree that there is no "throw-away" code, and that code in this PR is of high quality

Testing

I've tested the code using the following test programs (provide list here):

• sched_test_periodicity
• micro_booter
• unit_pingpong
• unit_schedtests
• ...(add others here)