elog-gen.py: Set INFO as default error log severity level

Some error yaml files in the phosphor-dbus-interfaces repo do not
specify the error log severity. Default this value to INFO.

Change-Id: Ifd335ba7d5e3e8238365036a2bfa7a199e014cfc
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
1 file changed