Ensure newlines are added between context config files

When multiple file_contexts, service_contexts and property_contexts
are processed by the m4(1) macro processor, they will fail if one
or more of the intermediate files final line is not terminated by
a newline. This patch adds an intervening file only containing a
newline.

Change-Id: Ie66b32fe477d08c69e6d6eb1725f658adc384ce4
Signed-off-by: Richard Haines <richard_c_haines@btinternet.com>