Force utf8 encoding in the javac args

I am working on a (Opscode) Chef cookbook to build opentsdb from source to ease the inhouse usage for our developpers.

I found an odd behaviour when compiling the **next** branch inside a chef run, where a lot of errors like "error: unmappable character for encoding ASCII" occured on some unit tests  (in TestJSON.java).

What is odd is that if I ssh into my VM and launch the build, everything is fine. If the build is part of a chef run, it fails (and yes, the **LANG** env var is set to **en_US.UTF-8** in all cases)

The patch that consists in adding **-encoding utf-8** to the javac flags fixes it.

As the unit tests explicitly use utf-8 encoded .java files, I'd like to propose this patch for everyone