Fix waiting for new events (elastic#10593) (elastic#10825)

* Adding more syscalls to the whitelist in `libbeat`
 I have removed the seccomp policy of `journalbeat`. Four new syscalls has been added to the common policy instead: `fstatfs`, `getrlimit`, `ppoll` and `splice`.
* Eliminate possible deadlock when closing the client
* Previously, `journalbeat` was unable to read new entries from the journal after it has been started. Now it is fixed, and the reader code is much simpler now.
* updated vendored `github.com/coreos/go-systemd/sdjournal` to latest release (no changes)

(cherry picked from commit 1dc58e0)

CHANGELOG.next.asciidoc

@@ -274,3 +274,6 @@ https://github.com/elastic/beats/compare/v6.6.0...6.x[Check the HEAD diff]
 
 ==== Known Issue
 
+*Journalbeat*
+
+- Journalbeat requires at least systemd v233 in order to follow entries after journal changes (rotation, vacuum).

NOTICE.txt

@@ -232,8 +232,8 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 --------------------------------------------------------------------
 Dependency: github.com/coreos/go-systemd
-Version: v17
-Revision: 39ca1b05acc7ad1220e09f133283b8859a8b71ab
+Version: v18
+Revision: 9002847aa1425fb6ac49077c0a630b3b67e0fbfd
 License type (autodetected): Apache-2.0
 ./vendor/github.com/coreos/go-systemd/LICENSE:
 --------------------------------------------------------------------

journalbeat/input/input.go

@@ -189,10 +189,10 @@ func (i *Input) publishAll() {
 
 // Stop stops all readers of the input.
 func (i *Input) Stop() {
-	i.client.Close()
 	for _, r := range i.readers {
 		r.Close()
 	}
+	i.client.Close()
 }
 
 // Wait waits until all readers are done.