Previously, cmakehdf5 turned on compiling of the java interface
by default due to a value set in cacheinit.cmake.

Now, consistent with how Fortran and CPP interfaces are handled,
the script overwrites this default value to disable the libraries,
fixing HDFGroup#2958.

I also implemented the --enable-java/--disable java options for
cmakehdf5, and -java for buildhdf5.

Allen said these scripts should mention that
compilers are to be specified in environment variables, but missing
compilers causes errors at the CMake level, and
CMake's error messages are already pretty informative (See the one
in HDFGroup#2958 about JAVA_COMPILER).