Add ability to specify interval-update value in vas.conf

This patch lets you specify the interval-update in the [vasd] section of
the vas.conf. The default is 600 (10 minutes) which is taken from the
man page.
Add ability to specify options for [libvas] in vas.conf

This adds the ability to specify the following and uses the default
values specified in the vas.conf man page.
 * use-dns-srv
 * use-tcp-only
 * auth-helper-timeout
Merge pull request #9 from ghoneycutt/add_libvas_options_to_vas_conf

Add libvas options to vas conf