Dev/add etcd implementation

[thangnguyen-69]

• Implement basic etcd lock with blocking strategies and lease.
• add basic testing for lock and lockprovider(passed) but the combinatorial test failed.

For #119

[madelson]

Really appreciate the great work @thangnguyen-69 !

I've gone through the code and detail and added a number of comments. I think there are a bunch of small things to do but overall the code looks pretty close!

2 other asks:

• Please document the local setup steps by adding them to this file on your branch. I'll use those to run the code locally
• Please add a docs page like this one for Etcd locks. You can follow the others for examples of what sort of information should go there.

[madelson]

the combinatorial test failed

• First off, don't worry about getting the tests to pass for every provider. Let's just try to get all the Etcd combinatorial tests passing
• If you're stuck, let me know which tests are failing and I can maybe offer suggestions on how to proceed.

[thangnguyen-69]

@madelson received your comments and i will work on it and notify back again for a 2nd round.