Don't emulate VGA on POWER KVM
Do not initialize Sound for the build VMs

QEMU by default initializes sound access, which is unnecessary
(we do not want to have sound devices, ever) and also hurts
performance on armv7l - the probing and spilling error messages
takes a bit of startup time.
Various KVM related fixes for armv7l

We do not want to hardcode the memsize but instead use
the host configuration. Also prefer the guest initrd
over the host initrd, as they might differ (and do)
Optimize VM image setup

These changes save over 5s on a VM setup phase of a typical
armv7l build. Instead of asking mkfs.ext4 to create a journal
(which is causing it to do flushed writes of lots of zero blocks)
and immediately deleting it afterwards, simply don't create it
initially. This alone saves 2s.

Prefering fallocate to make use of persistent preallocation
avoids fragmentation and small other fixes further speed up
the initial build setup phase by several seconds typically.
avoid a remount data=writeback on ext4

Won't work anyway, there is no journal. Silences a
warning.
Merge pull request #46 from k0da/master

Don't emulate VGA on POWER
Merge pull request #51 from dirkmueller/bug/armv7_fixes

Bug/armv7 fixes
Merge pull request #52 from dirkmueller/opt/vm_init_create

Optimize VM image setup