The IPA ramdisk and kernel images may be built or downloaded via a URL.
If the latter option is used, any images previously downloaded to
$KOLLA_CONFIG_PATH/config/ironic/ironic-agent.* would previously not be
updated if the image contents change.
This change introduces variables for setting a URL to a file containing
checksums for the images. The algorithm used to compute the checksum is
also configurable (default sha256). This allows us to ensure we are
using the correct version of the image, while avoiding an expensive few
hundred megabyte image download just to check.
If a checksum is not specified, the image will be downloaded every time
to ensure that it is up to date.
Change-Id: I8120518ed98d61f3652f5205ce7ec9f798ab2aa1
Story: 2001660
Task: 6693
ef84890798