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.
Merge pull request #2 from lotia/init-script-simplifications

Hadoop init script and rpm build simplifications.