MAHOUT-2085 Add scm tag for each pom.xml per ASF release guidelines

[andrewpalumbo]

Purpose of PR:

Please give a short description of what this PR is for.

Add SCM element to each POM per Apache Guidelines:

https://www.apache.org/dev/publishing-maven-artifacts.html

Important ToDos

Please mark each with an "x"

• [ x] A JIRA ticket exists (if not, please create this first)[https://issues.apache.org/jira/browse/mahout/]
• [x ] Title of PR is "MAHOUT-XXXX Brief Description of Changes" where XXXX is the JIRA number.
• [x ] Created unit tests where appropriate
• [x ] Added licenses correct on newly added files
• [ x] Assigned JIRA to self
• [ x] Added documentation in scala docs/java docs, and to website
• [ x] Successfully built and ran all unit tests, verified that all tests pass locally.

If all of these things aren't complete, but you still feel it is
appropriate to open a PR, please add [WIP] after MAHOUT-XXXX before the
descriptions- e.g. "MAHOUT-XXXX [WIP] Description of Change"

Does this change break earlier versions?
no
Is this the beginning of a larger project for which a feature branch should be made?
no

[andrewpalumbo]

merging without review for RC4