Make pam_loginuid.so optional for ssh

This is in line with current Docker examples and avoids errors
due to lack of CAP_AUDIT_WRITE or some other error encountered
while setting the process attribute.

Such errors would manifest as error messages like the following:
PAM: pam_open_session(): Cannot make/remove an entry for the specified session

docker/Dockerfile

@@ -11,7 +11,9 @@ RUN apt-get update -q \
       vim \
       nano \
       patch \
-      git-annex && rm -rf /var/lib/apt/lists/*
+      git-annex \
+    && rm -rf /var/lib/apt/lists/* \
+    && sed 's/session\s*required\s*pam_loginuid.so/session optional pam_loginuid.so/g' -i /etc/pam.d/sshd
 
 # Remove MOTD
 RUN rm -rf /etc/update-motd.d /etc/motd /etc/motd.dynamic