ASACORE-1132: Add support for sub-config files

Moved static content of generated config file to its own file that
includes the generated portion as well as any files under
/etc/alljoyn/gwagent/.

Change-Id: Ia23d5014aebbc80530303fee3947a272516e14e2
Signed-off-by: Steve Kinneberg <stevek@qce.qualcomm.com>