templates: Fix Debian 7.0 i386 template to use rc1 i386 release

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>
templates: Use cat to append or write multiline string to a file

The grub2 config patching fails and an empty file is written as echo <<EOF is
used. Using cat fixes the issue. Tested with vbox by creating veewee based
systemvm template for CloudStack [1]

[1] http://jenkins.cloudstack.org/job/build-systemvm-master

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>