[puppet] Increase maximum file descriptor count for zulip in limits.conf.

We ran into the 1024 file descriptor limit today for tornado.  The
limits.conf file descriptor limit isn't used for supervisor started as
we currently do it, but it's a good idea to have this in place so that
if we move supervisor to run as the zulip user, we don't experience a
nasty surprise.

(imported from commit 2eb4805b5c129bc2684d151b77f295c2eaa9fc3e)

servers/puppet/modules/zulip/files/limits.conf

@@ -0,0 +1,58 @@
+# /etc/security/limits.conf
+#
+#Each line describes a limit for a user in the form:
+#
+#<domain>        <type>  <item>  <value>
+#
+#Where:
+#<domain> can be:
+#        - an user name
+#        - a group name, with @group syntax
+#        - the wildcard *, for default entry
+#        - the wildcard %, can be also used with %group syntax,
+#                 for maxlogin limit
+#        - NOTE: group and wildcard limits are not applied to root.
+#          To apply a limit to the root user, <domain> must be
+#          the literal username root.
+#
+#<type> can have the two values:
+#        - "soft" for enforcing the soft limits
+#        - "hard" for enforcing hard limits
+#
+#<item> can be one of the following:
+#        - core - limits the core file size (KB)
+#        - data - max data size (KB)
+#        - fsize - maximum filesize (KB)
+#        - memlock - max locked-in-memory address space (KB)
+#        - nofile - max number of open files
+#        - rss - max resident set size (KB)
+#        - stack - max stack size (KB)
+#        - cpu - max CPU time (MIN)
+#        - nproc - max number of processes
+#        - as - address space limit (KB)
+#        - maxlogins - max number of logins for this user
+#        - maxsyslogins - max number of logins on the system
+#        - priority - the priority to run user process with
+#        - locks - max number of file locks the user can hold
+#        - sigpending - max number of pending signals
+#        - msgqueue - max memory used by POSIX message queues (bytes)
+#        - nice - max nice priority allowed to raise to values: [-20, 19]
+#        - rtprio - max realtime priority
+#        - chroot - change root to directory (Debian-specific)
+#
+#<domain>      <type>  <item>         <value>
+#
+
+#*               soft    core            0
+#root            hard    core            100000
+#*               hard    rss             10000
+#@student        hard    nproc           20
+#@faculty        soft    nproc           20
+#@faculty        hard    nproc           50
+#ftp             hard    nproc           0
+#ftp             -       chroot          /ftp
+#@student        -       maxlogins       4
+zulip		 soft	 nofile		 40000
+zulip		 hard	 nofile		 50000
+
+# End of file

servers/puppet/modules/zulip/manifests/base.pp

@@ -68,6 +68,14 @@ class zulip::base {
     source     => 'puppet:///modules/zulip/puppet.conf',
   }
 
+  file { '/etc/security/limits.conf':
+    ensure     => file,
+    mode       => 640,
+    owner      => "root",
+    group      => "root",
+    source     => 'puppet:///modules/zulip/limits.conf',
+  }
+
   file { '/etc/apt/apt.conf.d/02periodic':
     ensure     => file,
     mode       => 644,