The `grub2-mkconfig` tool is usually re-run when a new filesystem is
mounted so the new menuentry produced can be use on the next
boot. However the new created linux command (on the new entry)
has only the root parameter and it is invalid for mapper devices.
The proposed changes tries to source the grub's default environment file
if present so it can be used to create a more complete kernel command
line and fixes the kernel's root value, where it takes the symlink
instead of the cannonical file, allowing device mapper types to boot
in a consistent way.
Resolves: #RHEL-55234
Signed-off-by: Leo Sandoval <lsandova@redhat.com>
