Set default umask of 0027 for all Beats-created files (elastic#14119)

* Set umask of 027 (on non-windows systems) for all Beats-created files

* Fixing comment

* Update tests

* Updating docs for filebeat.registry.file_permissions

* Denoting octal

* Allow beats to override umask

* Removing accidentally-committed file

* Adding system test for default umask

* Make setUmask return error

* Defining ErrNotImplemented locally

* Defining not implemented error locally

* Fixing typo

* Skip umask test on Windows

* Adding missed imports

* Adding CHANGELOG entry

CHANGELOG.next.asciidoc

@@ -11,6 +11,16 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 *Affecting all Beats*
 
 - Update to Golang 1.12.1. {pull}11330[11330]
+- Update to Golang 1.12.4. {pull}11782[11782]
+- Update to ECS 1.0.1. {pull}12284[12284] {pull}12317[12317]
+- Default of output.kafka.metadata.full is set to false by now. This reduced the amount of metadata to be queried from a kafka cluster. {pull}12738[12738]
+- Fixed a crash under Windows when fetching processes information. {pull}12833[12833]
+- Update to Golang 1.12.7. {pull}12931[12931]
+- Remove `in_cluster` configuration parameter for Kuberentes, now in-cluster configuration is used only if no other kubeconfig is specified {pull}13051[13051]
+- Disable Alibaba Cloud and Tencent Cloud metadata providers by default. {pull}13812[12812]
+- Libbeat HTTP's Server can listen to a unix socket using the `unix:///tmp/hello.sock` syntax. {pull}13655[13655]
+- Libbeat HTTP's Server can listen to a Windows named pipe using the `npipe:///hello` syntax. {pull}13655[13655]
+- By default, all Beats-created files and folders will have a umask of 0027 (on POSIX systems). {pull}14119[14119]
 
 *Auditbeat*