Formal PR of some bug fixes and code improvements

[betahxy]

Summary of this Pull Request (PR)

This PR mainly includes some bug fixes, including:

1. Add support to multi-tenants Memcache application
2. Fix sync lock and blkpt bugs
3. Fix multi-core capability cacheline contention problem (TODO: improve this by putting the expanding logic in cos_cap_cpy_at)
4. Remove VGA support because it is not multi-thread safe
5. Fix some scheduling related bugs

   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.
• [x] 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) @gparmer @WenyuanShao @evanstella

Code Quality

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

Style:

• [x] Comments adhere to the Style Guide (SG)
• [x] Spacing adhere's to the SG
• [x] Naming adhere's to the SG
• [x] 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:

• [x] I've made an attempt to remove all redundant code
• [x] I've considered ways in which my changes might impact existing code, and cleaned it up
• [x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [x] I've commented appropriately where code is tricky
• [x] 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):

• [ ] micro_booter
• [ ] unit_pingpong
• [ ] unit_schedtests
• [ ] ...(add others here)