mysql: default to no root password (like 5.6).

Point the users to the relevant command so they can secure it more if
they wish.

Closes Homebrew/homebrew#46159.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/mysql.rb

@@ -134,18 +134,27 @@ class Mysql < Formula
     datadir.mkpath
     unless (datadir/"mysql/user.frm").exist?
       ENV["TMPDIR"] = nil
-      system bin/"mysqld", "--initialize", "--user=#{ENV["USER"]}",
+      system bin/"mysqld", "--initialize-insecure", "--user=#{ENV["USER"]}",
         "--basedir=#{prefix}", "--datadir=#{datadir}", "--tmpdir=/tmp"
     end
   end
 
-  def caveats; <<-EOS.undent
-    A "/etc/my.cnf" from another install may interfere with a Homebrew-built
-    server starting up correctly.
+  def caveats
+    s = <<-EOS.undent
+    We've installed your MySQL database without a root password. To secure it run:
+        mysql_secure_installation
 
-    To connect:
+    To connect run:
         mysql -uroot
     EOS
+    if File.exist? "/etc/my.cnf"
+      s += <<-EOS.undent
+
+        A "/etc/my.cnf" from another install may interfere with a Homebrew-built
+        server starting up correctly.
+      EOS
+    end
+    s
   end
 
   plist_options :manual => "mysql.server start"