Install Nova into its own venv

Install a couple of optional feature prereqs in hypervisor plugins.

rootwrap is horribly called indirectly via PATH.  The choice, other than fixing
such nonsense, is to force the path in sudo.

TODO:
* python guestfs isn't in pypi, need to specifically install it to not
  use the distro package

Change-Id: Iad9a66d8a937fd0b0d1874005588c702e3d75e04
diff --git a/files/debs/general b/files/debs/general
index 84d4302..87a6c7c 100644
--- a/files/debs/general
+++ b/files/debs/general
@@ -23,3 +23,4 @@
 libssl-dev # for pyOpenSSL
 gettext  # used for compiling message catalogs
 openjdk-7-jre-headless  # NOPRIME
+pkg-config