update zypper element

Scripts in pre-install.d run as root so there is no need to sudo commands.
This patch also helps avoid an error when sudo is not installed in the
default image.

Change-Id: Iab20edfb161189f8c4e0cfa7d6946f63163d6413
Ensure cache directory exists before use

Ensure cache mount directory exists before its used. The zypper element
would error when attempting to mount the cache directory because the
mount point did not exist. This patch corrects that.

Change-Id: Iaa3c2a0254b12bd847643a61a99f5a234097fd21
Add select-boot-kernel-initrd element

Encapsulate the new select-boot-kernel-initrd common function
into an element so other elements can make use of it.

Change-Id: Ie587bd5dae1afebfd5646190dfa951a7949938cd
Merge "update zypper element"
Merge "Ensure cache directory exists before use"
Merge "Add select-boot-kernel-initrd element"