Add support for syslog server hostname

schlagert/syslog version 3.4.3 adds support for specifying a host name for `dest_host`, this PR supports it as well

See this gist for my test procedure:

git@gist.github.com:7ab6348839c3dc7b18b6662f024e089c.git

Makefile

@@ -136,7 +136,7 @@ BUILD_DEPS = rabbitmq_cli
 DEPS = ranch syslog lager rabbit_common
 TEST_DEPS = rabbitmq_ct_helpers rabbitmq_ct_client_helpers amqp_client meck proper
 
-dep_syslog = git https://github.com/schlagert/syslog 3.4.2
+dep_syslog = git https://github.com/schlagert/syslog 3.4.3
 
 define usage_xml_to_erl
 $(subst __,_,$(patsubst $(DOCS_DIR)/rabbitmq%.1.xml, src/rabbit_%_usage.erl, $(subst -,_,$(1))))

priv/schema/rabbit.schema

@@ -1086,9 +1086,8 @@ end}.
     {datatype, {enum, [true, false]}}
 ]}.
 
-{mapping, "log.syslog.ip", "syslog.dest_host", [
-    {datatype, string},
-    {validators, ["is_ip"]}
+{mapping, "log.syslog.host", "syslog.dest_host", [
+    {datatype, string}
 ]}.
 
 {mapping, "log.syslog.port", "syslog.dest_port", [
@@ -1353,12 +1352,6 @@ fun(File) ->
     element(1, ReadFile) == ok
 end}.
 
-{validator, "is_ip", "string is a valid IP address",
-fun(IpStr) ->
-    Res = inet:parse_address(IpStr),
-    element(1, Res) == ok
-end}.
-
 {validator, "non_negative_integer", "number should be greater or equal to zero",
 fun(Int) when is_integer(Int) ->
     Int >= 0

test/config_schema_SUITE_data/rabbit.snippets

@@ -540,7 +540,7 @@ credential_validator.regexp = ^abc\\d+",
     log.syslog.identity = rabbitmq
     log.syslog.facility = user
     log.syslog.multiline_mode = true
-    log.syslog.ip = 10.10.10.10
+    log.syslog.host = 10.10.10.10
     log.syslog.port = 123",
    [
     {rabbit,[{log, [{syslog, [{enabled, true}]}]}]},
@@ -554,10 +554,12 @@ credential_validator.regexp = ^abc\\d+",
   {log_syslog_tcp,
    "log.syslog = true
     log.syslog.transport = tcp
-    log.syslog.protocol = rfc5424",
+    log.syslog.protocol = rfc5424
+    log.syslog.host = syslog.my-network.com",
    [
     {rabbit,[{log, [{syslog, [{enabled, true}]}]}]},
-    {syslog, [{protocol, {rfc5424, tcp}}]}
+    {syslog, [{protocol, {rfc5424, tcp}},
+              {dest_host, "syslog.my-network.com"}]}
    ],
    []},
   {log_syslog_udp_default,