Put RunJava.class in a jar, runjava.jar

We use the RunJava Java class to run Java applications (both java.so
and the "java" CLI command use it). We used to have RunJava.class
uncompressed, in the /java directory, but this caused two problems:

1. Or noticed that having a directory (/java) on the classpath causes
   thousands of stat() calls when Java tries to look for all classes
   in this directory. With a jar, its contents are read only once.

2. The "java" CLI command (java.groovy) didn't work because apparently
   Groovy cannot deal with classes being in the top-level package.

   So this patch moves RunJava into the io.osv package, and put it into a jar
   /java/runjava.jar.

   Note that java.groovy is changed in a separate patch (because it's in
   a different sub-repository....)

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>