support -l to export for specifying log root

export/upstart/master.conf.erb

@@ -1,8 +1,8 @@
 pre-start script
 
 bash << "EOF"
-  mkdir -p /var/log/<%= app %>
-  chown -R <%= user %> /var/log/<%= app %>
+  mkdir -p <%= log_root %>/<%= app %>
+  chown -R <%= user %> <%= log_root %>/<%= app %>
 EOF
 
 end script

export/upstart/process.conf.erb

@@ -3,4 +3,4 @@ stop on stopping <%= app %>-<%= process.name %>
 respawn
 
 chdir <%= engine.directory %>
-exec su <%= user %> -c "<%= process.command %> >> /var/log/<%=app%>/<%=process.name%>-<%=num%>.log 2>&1"
+exec su <%= user %> -c "<%= process.command %> >> <%= log_root %>/<%=app%>/<%=process.name%>-<%=num%>.log 2>&1"