clear out old execution system

[garlick]

0.12.0 will contain the first minimally viable version of our new execution system, and we intended to fork a 0.11.1 if we need to address issues in the old one to support our users.

Meanwhile we could clean the slate for 0.12.0 by removing the old stuff, including (I think!)

• src/modules/wreck
• src/common/libkz
• src/cmd/flux-wreck, flux-wreckrun, flux-submit, flux-jstat
• src/common/libjsc
• src/bindings/lua/wreck.lua, wreck/io.lua
• src/bindings/python/jsc.py, kz.py
• src/common/libzio
• various sharness tests and helper programs

[chu11]

As a side effect of removing the old exec system, I think we can remove:

• old kvs watch interface (modules/kvs, libkvs/kvs_watch, cmd/flux-kvs, various tests)
• libkvs: kvs-classic (as noted in Convert code to use new KVS functions and not KVS classic #1744, libkz, wrexec, are the biggest users)

And I'll throw in some potential issues that will go away as a side effect

#1980
#1625

[grondo]

I was already 80% done with this so I'll keep going. (it is basically git blame | grep grondo | rm -rf)

[grondo]

closed by #1988