IMPALA-8102: update Impala/HBase docs
IMPALA-8102: update Impala/HBase docs

Provide pointers to Kudu, which is generally better for analytics

Remove or reword advice that encourages people to use HBase for
analytics.

Remove incorrect information about joins resulting in single-row HBase
lookups - this simply doesn't happen.

Change-Id: If1d5f014722d35eab9b60f7a4e8479738f1bed5b
Reviewed-on: http://gerrit.cloudera.org:8080/12315
Tested-by: Impala Public Jenkins <039b6b20426ff68ebe492b3021890d8c8fd010c9@cloudera.com>
Reviewed-by: Alex Rodoni <b46da68bf9b818cec7052f7cdfe9b3e69485676b@cloudera.com>

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala