Set explicit -Xmx for Guava tests in pom.xml.

Also remove attempt to set the heap size in the Travis configuration
and change it around a little so Javadoc is generated in the install
step and not in the testing step.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79437983
Make GWT logging even quieter for Travis build.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=79441097