Install build deps for nodepool installation

Nodepool depend on pyzmq which requires a C and C++ compiler chain.
Nodepool also has a transitive dep on cryptography which depends on
libffi-dev being available. Finally cryptography also depends on
libssl-dev for its building. Install build-essential for the compiler
chain and libffi-dev/libssl-dev to make cryptography work prior to
installing nodepool.

Change-Id: If32f6fd868ea9fefca2df610e9a2cb7a06a78631

modules/nodepool/manifests/init.pp

@@ -73,6 +73,9 @@ class nodepool (
   }
 
   $packages = [
+    'build-essential',
+    'libffi-dev',
+    'libssl-dev',
     'kpartx',
     'qemu-utils',
   ]
@@ -126,6 +129,9 @@ class nodepool (
     subscribe   => Vcsrepo['/opt/nodepool'],
     require     => [
       Class['pip'],
+      Package['build-essential'],
+      Package['libffi-dev'],
+      Package['libssl-dev'],
       Package['python-lxml'],
     ],
   }