refactor System.[g/s]etProperty(...) calls.  instead use MasterConf .[g/s]etProperty(..) calls.

This pull removes environment variable handling from the code.  It does not move the existing System properties to config files (left for next refactor).

Everything is funneled to the MasterConfig class which uses Utils.getProperty(..) setProperty() to change properties.  The property weight is maintained for both get and set:  system > .properties > hadoop config
If you look at `TachyonWorker#main` the hostname is given from CLI and `NetworkUtils.resolveHostName` is used.

Should worker be updated, or should this be moved out of utils since it only matters for master?