Makes owncloud uses Mail variables from ENV

dockerfiles/services/nginx-php/ssmtp.conf

-mailhub=172.17.42.1
-root=postmaster
+mailhub=##MAIL_HOST##:##MAIL_PORT##
+root=##MAIL_USER##
 FromLineOverride=YES
 
+# Use SSL/TLS before starting negotiation
+UseTLS=Yes
+UseSTARTTLS=Yes
+
+# Username/Password
+AuthUser=##MAIL_USER##
+AuthPass=##MAIL_PASS##
+

dockerfiles/services/owncloud/startup-owncloud.sh

 #!/bin/bash -eux
+
+### configure email
+sed -i s/##MAIL_HOST##/${MAIL_HOST}/ /etc/ssmtp/ssmtp.conf
+sed -i s/##MAIL_PORT##/${MAIL_PORT}/ /etc/ssmtp/ssmtp.conf
+sed -i s/##MAIL_USER##/${MAIL_USER}/ /etc/ssmtp/ssmtp.conf
+sed -i s/##MAIL_PASS##/${MAIL_PASS}/ /etc/ssmtp/ssmtp.conf
+
 ###
 # Check Pre Install
 ###