POM-9. Upgrade to Avro 1.7.5

issue: https://jira.kiji.org/browse/POM-9
review: https://review.kiji.org/r/997
SCHEMA-757. Update REVIEWERS file in kiji-avro.

issue: https://jira.kiji.org/browse/SCHEMA-757
review: https://review.kiji.org/r/1809
Depends on mr1 cdh5.0.3 jars.
More pom file tweaks.