HBASE-19983 update Hadoop support matrix for Hadoop releases 2.8.2+ and 2.9.0.

Signed-off-by: Mike Drob <mdrob@apache.org>

Author: busbey

src/main/asciidoc/_chapters/configuration.adoc

@@ -215,8 +215,9 @@ Use the following legend to interpret this table:
 |Hadoop-2.6.1+ | S | S | S
 |Hadoop-2.7.0 | X | X | X
 |Hadoop-2.7.1+ | S | S | S
-|Hadoop-2.8.0 | X | X | X
-|Hadoop-2.8.1 | X | X | X
+|Hadoop-2.8.[0-1] | X | X | X
+|Hadoop-2.8.2+ | NT | NT | NT
+|Hadoop-2.9.0 | X | X | X
 |Hadoop-3.0.0 | NT | NT | NT
 |===
 
@@ -238,16 +239,10 @@ HBase on top of an HDFS Encryption Zone. Failure to do so will result in cluster
 data loss. This patch is present in Apache Hadoop releases 2.6.1+.
 ====
 
-.Hadoop 2.7.x
+.Hadoop 2.y.0 Releases
 [TIP]
 ====
-Hadoop version 2.7.0 is not tested or supported as the Hadoop PMC has explicitly labeled that release as not being stable. (reference the link:https://s.apache.org/hadoop-2.7.0-announcement[announcement of Apache Hadoop 2.7.0].)
-====
-
-.Hadoop 2.8.x
-[TIP]
-====
-Hadoop version 2.8.0 and 2.8.1 are not tested or supported as the Hadoop PMC has explicitly labeled that releases as not being stable. (reference the link:https://s.apache.org/hadoop-2.8.0-announcement[announcement of Apache Hadoop 2.8.0] and link:https://s.apache.org/hadoop-2.8.1-announcement[announcement of Apache Hadoop 2.8.1].)
+Starting around the time of Hadoop version 2.7.0, the Hadoop PMC got into the habit of calling out new minor releases on their major version 2 release line as not stable / production ready. As such, HBase expressly advises downstream users to avoid running on top of these releases. Note that additionally the 2.8.1 was release was given the same caveat by the Hadoop PMC. For reference, see the release announcements for link:https://s.apache.org/hadoop-2.7.0-announcement[Apache Hadoop 2.7.0], link:https://s.apache.org/hadoop-2.8.0-announcement[Apache Hadoop 2.8.0], link:https://s.apache.org/hadoop-2.8.1-announcement[Apache Hadoop 2.8.1], and link:https://s.apache.org/hadoop-2.9.0-announcement[Apache Hadoop 2.9.0].
 ====
 
 .Replace the Hadoop Bundled With HBase!