Hadoop init script and rpm build simplifications.

- Multiple hadoop init scripts are now replaced by a single script to
which a symlink is created for each hadoop component type.

- The hadoop maven pom.xml was modified to create the symlinks.

- The init script now explicitly appends the ${JAVA_HOME}/bin directory
to the hadoop user's PATH and sets hadoop JAVA_HOME to the value of the
${JAVA_HOME} env var set in the init script. This ensures that any value
that is defined in the hadoop user's environment doesn't overwrite
the values specified in the init script.