Extend default SAML IdP metadata validity period

Extend default SAML IdP metadata validity period

Our current default IdP metadata validity period is hardcoded to 30
days.  This is very limiting for anything other than a test environment
unless there is a way to allow SPs to automatically fetch updated metadata
on a regular interval.

This patch increases the default validity period to 5 years.  In addition,
a new option for ipsilon-server-install is provided to allow a different
validity period to be specified.

https://fedorahosted.org/ipsilon/ticket/103
Signed-off-by: Nathan Kinder <nkinder@redhat.com>
Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>