HADOOP-11194. Ignore .keep files (kasha)

(cherry picked from commit d5084b9fa30771bffb03f2bad69304141c6e4303)

.gitignore

@@ -3,6 +3,7 @@
 *.iws
 *.orig
 *.rej
+**/.keep
 .idea
 .svn
 .classpath

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

@@ -297,6 +297,8 @@ Release 2.6.0 - UNRELEASED
     HADOOP-10681. Remove unnecessary synchronization from Snappy & Zlib
     codecs. (Gopal Vijayaraghavan via acmurthy)
 
+    HADOOP-11194. Ignore .keep files. (kasha)
+
   BUG FIXES
 
     HADOOP-11182. GraphiteSink emits wrong timestamps (Sascha Coenen via raviprak)