[SPARK-3437][BUILD] Support crossbuilding in maven.

This patch get rid of _2.10 in the artifact ids and adapts the install plugin to include it instead.
This will make it easy to cross build for scala 2.10 and 2.11.

There was no way(I know) to avoid copying the same code everywhere. (Maven oddities... )
I just checked the published pom had, just this inside it.
```xml
<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.apache.spark</groupId>
  <artifactId>spark-core_2.10</artifactId>
  <version>1.2.0-SNAPSHOT</version>
  <description>POM was created from install:install-file</description>
</project>
```

No dependency information, I am not sure if we can live without that.