Implement a simple "hello world" web server in Python and hook it into
SlapOS infrastructure, so that newcomers can see how to implement
SlapOS services:

    - start service from under etc/service/
    - add promise for service monitoring
    - publish connection url

TODO IPv4 frontend
------------------

For now the service is only accessible via IPv6, because SlapOS provides
an unique ipv6-address to every computer partition, and provided IPv4
addresses have non-global scope and can be used only for organizing
internal subservices.

The way we handle IPv4 publish - is through explicit additional IPv4
frontend - TODO add example how to do it.

TODO monitoring
---------------

Currently in SlapOS for a service in order to be monitorable, the
service needs to explicitly extend from monitoring stack:

    http://git.erp5.org/gitweb/slapos.git/blob/HEAD:/stack/monitor/README.txt

TODO - add example how to do it.

Cc: Jérome Perrin <jerome@nexedi.com>

Because partition IPv4 address(es) are not global ones - i.e. 10.0.12.57
- so we cannot expose a service through them to the world without
additional frontent proxy.

So let's leave only IPv6 listening address in the example.

Cc: Jérome Perrin <jerome@nexedi.com>

This reverts the essence of commit 854e4766:

Changing there

    ${instance-parameter:ipv6-random}

to

    ${instance-parameter:global-ipv6}

was wrong - slapos.cookbook:slapconfiguration recipe, which is leveraged
by [instance-parameter] section does not define global-ipv6:

    http://git.erp5.org/gitweb/slapos.git/blob/HEAD:/slapos/recipe/slapconfiguration.py?js=1#l70

- only ipv6 as "Set of IPv6 addresses (of partition)" and ipv6-random
"One of the IPv6 addresses".

Trying to instantiate a helloworld SR inside webrunner:

    ---- 8< ---- (instance.log)
    ...
    [2015-04-26 11:56:20,133] INFO Error: Referenced option does not exist: instance-parameter global-ipv6
    ...

and the same error while instantiating helloworld SR without slaprunner
under local slapproxy.

~~~~

The global-ipv6 is helpfully injected by slapos.cookbook:softwaretype
recipe into [slap-network-information] section:

    http://git.erp5.org/gitweb/slapos.git/blob/HEAD:/slapos/recipe/softwaretype.py?js=1#l164

but unfortunately only if that slapos.cookbook:softwaretype recipe is
activated - i.e. when we have several software types and we support switching
between them, which is not the case for helloworld (and it's a pity that
such fundamental network-configuration is only optionally provided by SlapOS).

~~~~

So let's switch back to ${instance-parameter:ipv6-random} - this way
helloworld instance can be instantiated again.

Cc: Jérome Perrin <jerome@nexedi.com>

kvm_run script can now create external disk with specified format (qcow2, raw, etc...)
if kvm external disk is created it will never be replaced, even if user
reduce the number of disk with parameter 'external-disk-number' or change the
'external-disk-format' value. All created disk will be added to qemu run command.

numa option can be used to create [fake] numa nodes and expose them to the guest
OS instance. In this case it is important to know the host cpu topology and where
the instance will be allocated.

cpu-options are additional parameters like sockets=1,cores=5,threads=1
in this case if cpu-count parameter is 1 qemu options will be:
-smp 1,sockets=1,cores=5,threads=1