[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... )
Sean I think this approach actually modifies the published pom's to look different than the poms which are our own build. I.e. it appends the 2.11 or 2.10 suffix to the artifact in the published poms. Other than being horrendously verbose... this does seem to be a nicer approach IMO.

Since donstream projects only consume spark via the published poms, it seems okay to me. What is the specific case you're concerned about?