Test class BuildEnvironmentIntegrationTest fails on linux without jdk5

Building :integTest:integTest on a linux system with jdk7 without one of
the following paths existing fails
/opt/jdk/sun-jdk-5, /opt/jdk/sun-jdk-6, /opt/jdk/ibm-jdk-6,
/opt/jdk/oracle-jdk-7, /opt/jdk/oracle-jdk-7
The @IgnoreIf({ AvailableJavaHomes.differentJdk == null}) in the test class
gives an expeption because of Jdk7FileCanonicalizer throwing an exception
if the file to canonicalize does not exist.
Mark a few toolingApi stories as DONE.
Restrict maxParallelForks to 2 for :toolingApi:integTest.

This avoids IllegalAccessError from Javac (GRADLE-3144) that
broke SamplesToolingApiIntegrationTest.