Release process for 2.7.1: Set the release date for 2.7.1.

(cherry picked from commit bf89ddb9b8ca27a34074b415f85599dd48b8fc50)

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -454,7 +454,7 @@ Release 2.7.2 - UNRELEASED
 
   BUG FIXES
 
-Release 2.7.1 - UNRELEASED
+Release 2.7.1 - 2015-07-06 
 
   INCOMPATIBLE CHANGES
 

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -688,7 +688,7 @@ Release 2.7.2 - UNRELEASED
 
   BUG FIXES
 
-Release 2.7.1 - UNRELEASED
+Release 2.7.1 - 2015-07-06 
 
   INCOMPATIBLE CHANGES
 

hadoop-mapreduce-project/CHANGES.txt

@@ -278,7 +278,7 @@ Release 2.7.2 - UNRELEASED
     MAPREDUCE-6425. ShuffleHandler passes wrong "base" parameter to getMapOutputInfo
     if mapId is not in the cache. (zhihai xu via devaraj)
 
-Release 2.7.1 - UNRELEASED
+Release 2.7.1 - 2015-07-06 
 
   INCOMPATIBLE CHANGES
 

hadoop-yarn-project/CHANGES.txt

@@ -562,7 +562,7 @@ Release 2.7.2 - UNRELEASED
     YARN-3508. Prevent processing preemption events on the main RM dispatcher. 
     (Varun Saxena via wangda)
 
-Release 2.7.1 - UNRELEASED
+Release 2.7.1 - 2015-07-06 
 
   INCOMPATIBLE CHANGES