Add Open3.popen3 wrapper that replaces ` and %x
Use the Cmd wrapper instead of backticks and %x
Fix cmd injection in NodeObject#bmc_cmd

Pass arguments to system separately, to prevent shell
expansion.
Move const_get calls to a protected method in a helper, include where needed
Update json gem to 1.6.8, which fixes a DoS vuln
Fix unescaped user input in views