vmdk: Update checks for 'vmdk' to include 'vmdk.xz'

vmdk: Update checks for 'vmdk' to include 'vmdk.xz'

Given that we now default to creating vmdk.xz rather than vmdk files we
need to ensure that when we check for 'vmdk' we also check for
'vmdk.xz'.

Bug-AGL: SPEC-775, SPEC-776
Change-Id: Ie2fba86edacade949a0c5146cd34abf4067a023b
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/11215
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>