Force uWSGI to set "Connection: close" header

uWSGI is currently not compliant with RFC 2616 section 14.10.
This will work around the problem by blindly applying the
correct header to responses, when using the default uWSGI
vassal configuration files. This does break persistent connections
in that case, so these configs should probably be changed for
production use (or uWSGI should not be used).

Change-Id: I56036768c46f1f727b10c7d231c3470dfa8213ea

etc/barbican/vassals/barbican-admin.ini

@@ -8,3 +8,4 @@ no-default-app = true
 memory-report = true
 plugins = python
 paste = config:/etc/barbican/barbican-admin-paste.ini
+add-header = Connection: close

etc/barbican/vassals/barbican-api.ini

@@ -8,3 +8,4 @@ no-default-app = true
 memory-report = true
 plugins = python
 paste = config:/etc/barbican/barbican-api-paste.ini
+add-header = Connection: close