Add pid: host to libvirt

Without pid: host, nova-compute and libvirt fail to operate correctly
together.  I don't understand why, and I wish it weren't so, but it means
folks will have to install docker-compose from my personal github account
until the pull request is merged upstream.

Change-Id: I24e55405139c831f2df246f54c5b6fd39d00656a

compose/nova-compute-network.yml

@@ -2,6 +2,7 @@ libvirt:
    image: kollaglue/centos-rdo-nova-libvirt
    name: libvirt
    net: host
+   pid: host
    privileged: true
    restart: always
    env_file:
@@ -33,7 +34,6 @@ novacompute:
    image: kollaglue/centos-rdo-nova-compute
    name: nova-compute
    net: host
-   pid: host
    privileged: true
    restart: always
    env_file:

docs/developer-env.md

 # Developer env
 
+In order to run Kolla, it is mandatory to run a version of
+`docker-compose` that includes pid: host support.  One of the
+authors of kolla has a pull request outstanding that the
+docker-compose maintainers have said they would merge shortly.
+
+It must be retrieved via git and installed:
+
+    git pull http://github.com/sdake/fig
+    cd fig
+    sudo pip install .
+    sudo pip install -U docker-py
+
 The basic starting environment will be created using `docker-compose`.
 This environment will start up the openstack services listed in the
 compose directory.