HADOOP-8857. hadoop.http.authentication.signature.secret.file docs should not state that secret is randomly generated. (tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1438601 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of github.com:griddynamics/yhadoop-common into trunk-gd
Merge branch 'trunk-gd' of github.com:griddynamics/yhadoop-common into fb-xxx-hadoop-auth-kerberos-realm-trunk-gd