Explicitly defined options as strings.

This fixes an issue where PyYAML was converting yes and no into True and False in the generated sshd_config file.

pillar.example

@@ -5,30 +5,30 @@ sshd_config:
     - /etc/ssh/ssh_host_rsa_key
     - /etc/ssh/ssh_host_dsa_key
     - /etc/ssh/ssh_host_ecdsa_key
-  UsePrivilegeSeparation: yes
+  UsePrivilegeSeparation: 'yes'
   KeyRegenerationInterval: 3600
   ServerKeyBits: 768
   SyslogFacility: AUTH
   LogLevel: INFO
   LoginGraceTime: 120
-  PermitRootLogin: yes
-  PasswordAuthentication: no
-  StrictModes: yes
-  RSAAuthentication: yes
-  PubkeyAuthentication: yes
-  IgnoreRhosts: yes
-  RhostsRSAAuthentication: no
-  HostbasedAuthentication: no
-  PermitEmptyPasswords: no
-  ChallengeResponseAuthentication: no
-  X11Forwarding: yes
+  PermitRootLogin: 'yes'
+  PasswordAuthentication: 'no'
+  StrictModes: 'yes'
+  RSAAuthentication: 'yes'
+  PubkeyAuthentication: 'yes'
+  IgnoreRhosts: 'yes'
+  RhostsRSAAuthentication: 'no'
+  HostbasedAuthentication: 'no'
+  PermitEmptyPasswords: 'no'
+  ChallengeResponseAuthentication: 'no'
+  X11Forwarding: 'yes'
   X11DisplayOffset: 10
-  PrintMotd: no
-  PrintLastLog: yes
-  TCPKeepAlive: yes
+  PrintMotd: 'no'
+  PrintLastLog: 'yes'
+  TCPKeepAlive: 'yes'
   AcceptEnv: "LANG LC_*"
   Subsystem: "sftp /usr/lib/openssh/sftp-server"
-  UsePAM: yes
+  UsePAM: 'yes'
 
 openssh:
   auth: