Generate plugins list through https requests

The devstack plugins list can be generated through web requests in
environments (such as the proposal slave) that lack copies of all
the relevant git repositories.

One downside to this is that there is no way of getting the last
modification time of the plugin.

Change-Id: I2c5c9282a8ad80014cad171a4dfbdc8f26044cd1
diff --git a/data/devstack-plugins-registry.header b/data/devstack-plugins-registry.header
index 9f8a994..687db04 100644
--- a/data/devstack-plugins-registry.header
+++ b/data/devstack-plugins-registry.header
@@ -14,6 +14,6 @@
 namespace, which includes but is not limited to official OpenStack
 projects.
 
-+------------------+------------------------------------------------------------+------------+
-|Plugin Name       |URL                                                         |Date        |
-+------------------+------------------------------------------------------------+------------+
++------------------+-------------------------------------------------------------------------+
+|Plugin Name       |URL                                                                      |
++------------------+-------------------------------------------------------------------------+