[accumulo] remove EOM Accumulo versions (1.6, 1.7) and rename 1.8 binding to 1.9. (#1366)

accumulo1.6/pom.xml

...6/src/main/java/site/ycsb/db/accumulo/AccumuloClient.java

accumulo1.6/src/test/resources/log4j.properties

accumulo1.7/README.md

accumulo1.7/pom.xml

accumulo1.7/src/main/conf/accumulo.properties

...1.7/src/main/java/site/ycsb/db/accumulo/package-info.java

...1.7/src/test/java/site/ycsb/db/accumulo/AccumuloTest.java

accumulo1.8/README.md

accumulo1.8/src/main/conf/accumulo.properties

...8/src/main/java/site/ycsb/db/accumulo/AccumuloClient.java

...1.8/src/main/java/site/ycsb/db/accumulo/package-info.java

...1.8/src/test/java/site/ycsb/db/accumulo/AccumuloTest.java

accumulo1.8/src/test/resources/log4j.properties

accumulo1.9/README.md

accumulo1.9/pom.xml

accumulo1.9/src/main/conf/accumulo.properties

...9/src/main/java/site/ycsb/db/accumulo/AccumuloClient.java

...1.9/src/main/java/site/ycsb/db/accumulo/package-info.java

...1.9/src/test/java/site/ycsb/db/accumulo/AccumuloTest.java