aarch64: Add kpti=off similar to x86_64 nopti

aarch64: Add kpti=off similar to x86_64 nopti

arm64 kernels use a different kernel option (kpti=off vs nopti) to
disable PTI, so sync the two platform configurations.

Conveniently, this also bypasses kernel 4.15 issues described in [1],
so apply the kernel option customisation via MaaS too, to allow aarch64
deployments to bootstrap using 4.15 kernel (with the downside of these
args being duplicated by Salt later in HA scenarios).

PTI is now disabled for baremetal nodes (via MaaS, no matter the
scenario) and/or for kvm/cmp hosts (in HA scenarios only).

While at it, install missing thin provisioning tools in aarch64
bootstrap image for MaaS deploy stage to succeed.

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1857074

Change-Id: Ibd1f57f24abc690b0f13b6298f25d7e8a1af1567
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>