Enable publishing to Sonatype Nexus repo

Heavily inspired from:
725f2c98f8a0960c66c291941acce992ec10d159
Add list of Hive dependencies, now that it's in Maven Central.
Excluse ASM 3.1 from Hive.

We want the transitive dependency from Spark's ASM 4.0.
Exclude Xerces pulled in from Hive.

It conflicts with JAXP's version.
Exclude Datanucleus for assembly only.

Also some cleanup.
Merge pull request #271 from harveyfeng/publish

Enable publishing to Sonatype Nexus repo