JSON load balancer config file

[andreaseno]

Replaced the server.conf file inside the load balancer nf with a json file called server.json. Because the config file parser was written for a plaintext file rather than a json file, I had to rewrite the backend config file parse function. It now uses cjson to parse the config file.

Summary:

Usage:

This PR includes
Resolves issues
Breaking API changes
Internal API changes
Usability improvements
Bug fixes
New functionality	x
New NF/onvm_mgr args
Changes to starting NFs	x
Dependency updates
Web stats updates

Merging notes:

• Dependencies: Should be merged after pull request #327 for the weighted policy, since this code includes code from that pull request.

TODO before merging :

• [x] PR is ready for review

Test Plan:

I tested the changes by doing a full setup of a 2 server ONVM experiment, made sure the arp_response and load balancer nf's ran correctly without error, and used iperf to verify that the packets would still send correctly. The only other necessary testing I can think of off the top of my head is verifying it works with more than 2 servers.

Review:

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[twood02]

@andreaseno I merged #327 so now you will need to resolve conflicts.

[twood02]

@andreaseno @xwedea I added a couple more changes. If you can fix them sometime in the next few weeks - great! If not I'll get another student to help out later.