PARQUET-121: Allow Parquet to build with Java 8

[tomwhite]

There are test failures running with Java 8 due to http://openjdk.java.net/jeps/180 which changed retrieval order for HashMap.

Here's how I tested this:

use-java8  
mvn clean install -DskipTests -Dmaven.javadoc.skip=true 
mvn test
mvn test -P hadoop-2

I also compiled the main code with Java 7 (target=1.6 bytecode), and compiled the tests with Java 8, and ran them with Java 8. The idea here is to simulate users who want to run Parquet with JRE 8.

use-java7
mvn clean install -DskipTests -Dmaven.javadoc.skip=true 
use-java8 
find . -name test-classes | grep target/test-classes | grep -v 'parquet-scrooge' | xargs rm -rf
mvn test -DtargetJavaVersion=1.8 -Dmaven.main.skip=true -Dscala.maven.test.skip=true

A couple of notes about this:

• The targetJavaVersion property is used since other Hadoop projects use the same name.
• I couldn’t get parquet-scrooge to compile with target=1.8, which is why I introduced scala.maven.test.skip (and updated scala-maven-plugin to the latest version which supports the property). Compiling with target=1.8 should be fixed in another JIRA as it looks pretty involved.

[rdblue]

Is this needed to add the scala.maven.test.skip property, or is this related to other fixes?

[tomwhite]

It's needed for skip.

[rdblue]

I've tested this as Tom suggested and everything passes. Strangely, I didn't skip the scala tests or remove test classes from parquet-scrooge and everything still passed. I tested the build target=1.6 with tests targeting 1.6 (in java7) and 1.8 (in java8). Those work without modification. I also tested build target=1.8 with tests targeting 1.8 in java8 and all of the tests pass.

I think this PR is safe to merge.