ApacheSSLContext.enable_modules produces unnecessary output

[ajkavanagh]

This context function (which is run everytime the class instance is used) generates the following output:

Considering dependency setenvif for ssl:
Module setenvif already enabled
Considering dependency mime for ssl:
Module mime already enabled
Considering dependency socache_shmcb for ssl:
Module socache_shmcb already enabled
Module ssl already enabled
Module proxy already enabled
Considering dependency proxy for proxy_http:
Module proxy already enabled
Module proxy_http already enabled
Module headers already enabled

The function responsible is:

class ApacheSSLContext(OSContextGenerator):                                              

    ...

                                                                                  
     def enable_modules(self):                                                    
         cmd = ['a2enmod', 'ssl', 'proxy', 'proxy_http', 'headers']               
         check_call(cmd) 

If this were changed to:

     def enable_modules(self):                                                    
         cmd = ['a2enmod', 'ssl', 'proxy', 'proxy_http', 'headers', '1>/dev/null']               
         check_call(cmd, shell=True)

then the standard cruft would go, but we'd still get error messages. Thoughts?