Migrated configuration to a standalone file.

The deployed configuration file (xo-install.cfg) is not tracked by git,
so changes made by users won't affect their ability to update this git
repo.

sample.xo-install.cfg

@@ -0,0 +1,23 @@
+# Optional user that runs the service. root by default
+#XOUSER="node"
+
+# Port number where xen-orchestra service is bound
+PORT="80"
+
+# Base dir for installation and future updates
+INSTALLDIR="/etc/xo"
+
+# Git branch or tag (append tags/ before the tag name) where xen-orchestra sources are fetched
+BRANCH="master"
+
+# Log path for possible errors
+LOGFILE="$(dirname $0)/xo-install.log"
+
+# comma separated list of plugins to be installed, check README for more information
+#PLUGINS="xo-server-transport-email,xo-server-usage-report,xo-server-perf-alert"
+
+# NodeJS and Yarn are automatically updated when running update. Switch this option to false if you want to disable it.
+AUTOUPDATE="true"
+
+# Define the number of previous installations you want to keep. Needs to be at least 1
+PRESERVE="3"