EMR Bootstrap integration script fixes.

The current bootstrap integration script does not work with enterprise tarballs. The change below fixes it:
RELEASE_UNZIP=`ls -d /opt/alluxio*`
sudo mv $RELEASE_UNZIP /opt/alluxio

The current bootstrap integration script hardcodes a memory allocation. Alluxio workers are unable to start if an instance type with a smaller allocation is selected. Specifying this as a parameter would improve the user experience.