install: options for syslog and context

bug 1112831
https://bugzilla.redhat.com/show_bug.cgi?id=1112831

The administrative guide describes how to enable centralized logging.
This enhancement adds options to deploy with this configuration.
install: add yum_exclude_pkgs option

Sometimes we work with large yum repos that can be incompletely synced
such that the indices point to files that aren't there yet. Work around
this during development installs by simply excluding problem packages.