Since 76b644c3 when the support for RAM filesystems was introduced,
libvirt accepted the following XML:
<source usage='1024' unit='KiB'/>

This was parsed correctly and internally stored in bytes, but it
was formatted as (with an extra 's'):
<source usage='1024' units='KiB'/>
When read again, this was treated as if the units were missing,
meaning libvirt was unable to parse its own XML correctly.

The usage attribute was documented as being in KiB, but it was not
scaled if the unit was missing. Transient domains still worked,
because this was balanced by an extra 'k' in the mount options.

This patch:
Changes the parser to use 'units' instead of 'unit', as the latter
was never documented (fixing persistent domains) and some programs
(libvirt-glib, libvirt-sandbox) already parse the 'units' attribute.

Removes the extra 'k' from the tmpfs mount options, which is needed
because now we parse our own XML correctly.

Changes the default input unit to KiB to match documentation, fixing:
https://bugzilla.redhat.com/show_bug.cgi?id=1015689

The <filesystem> element can now accept a <driver type='nbd'/>
as an alternative to 'loop'. The benefit of NBD is support
for non-raw disk image formats.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

Extend the <driver> element in filesystem devices to
allow a storage format to be set. The new attribute
uses 'format' to reflect the storage format. This is
different from the <driver> element in disk devices
which use 'type' to reflect the storage format. This
is because the 'type' attribute on filesystem devices
is already used for the driver backend, for which the
disk devices use the 'name' attribute. Arggggh.

Anyway for disks we have

   <driver name="qemu" type="raw"/>

And for filesystems this change means we now have

   <driver type="loop" format="raw"/>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

This patch removes the emulatorRequired field and associated
infrastructure from the virCaps object. Instead the driver specific
callbacks are used as this field isn't enforced by all drivers.

This patch implements the appropriate callbacks in the qemu and lxc
driver and moves to check to that location.

<vcpu> is not an optional node. The value for its 'placement'
actually always defaults to 'static' in the underlying codes.
(Even no 'cpuset' and 'placement' is specified, the domain
process will be pinned to all the available pCPUs).

Pass argv to the init binary of LXC, using a new <initarg> element.

* docs/formatdomain.html.in: Document <os> usage for containers
* docs/schemas/domaincommon.rng: Add <initarg> element
* src/conf/domain_conf.c, src/conf/domain_conf.h: parsing and
  formatting of <initarg>
* src/lxc/lxc_container.c: Setup LXC argv
* tests/Makefile.am, tests/lxcxml2xmldata/lxc-systemd.xml,
  tests/lxcxml2xmltest.c, tests/testutilslxc.c,
  tests/testutilslxc.h: Test parsing/formatting of LXC related
  XML parts