postinst_intercepts: add a delay_to_first_boot hook
This allows postinsts scripts to explicitly request a deferral to first boot
(by calling 'postinst_intercept delay_to_first_boot') instead of 'exit 1' which
should be used only to indicate actual script failures.
Signed-off-by: Alexander Kanavin <alexander.kanavin@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>