MDEV-19123 Change default charset from latin1 to utf8mb4

Changing the default server character set from latin1 to utf8mb4.

mysql-test/include/check-warnings.inc

@@ -0,0 +1,68 @@
+#
+# This test is executed once after each test to check the servers
+# for unexpected warnings found in the servers error log
+#
+# NOTE! mysql-test-run.pl has already done a rough filtering
+# of the file and written any suspicious lines
+# to $error_log.warnings file
+#
+--disable_query_log
+
+# Don't write these queries to binlog
+set SQL_LOG_BIN=0;
+
+# Do not replicate updates to other galera nodes
+--error 0,1193
+set WSREP_ON=0;
+
+# Turn off any debug crashes, allow the variable to be
+# non existent in release builds
+--error 0,1193
+set debug_dbug="";
+
+use mtr;
+# Allow this session to read-write even if server is started
+# with --transaction-read-only
+set session transaction read write;
+
+create temporary table error_log (
+  row int auto_increment primary key,
+  suspicious int default 1,
+  file_name varchar(255),
+  line varchar(1024) default null
+) engine=myisam charset=latin1;
+
+# Get the name of servers error log
+let $log_error= $MTR_LOG_ERROR;
+let $log_warning= $log_error.warnings;
+
+# Try to load the warnings into a temporary table,
+# it might fail with error saying "The MySQL server is
+# running with the --secure-file-priv" in which case
+# an attempt to load the file using LOAD DATA LOCAL is made
+--error 0,1290
+eval load data infile '$log_warning' into table error_log character set latin1
+  fields terminated by 'xykls37' escaped by ''
+  ignore 1 lines
+  (line)
+  set file_name='$log_error';
+
+if ($mysql_errno)
+{
+  # Try LOAD DATA LOCAL
+  eval load data local infile '$log_warning' into table error_log
+    fields terminated by 'xykls37' escaped by ''
+    ignore 1 lines
+    (line)
+    set file_name='$log_error';
+}
+
+# Call check_warnings to filter out any warning in
+# the error_log table
+call mtr.check_warnings(@result);
+if (`select @result = 0`){
+  skip OK;
+}
+--enable_query_log
+echo ^ Found warnings in $log_error;
+exit;