available_apps redirects to https

While looking at the caching behavior I noticed that we currently automatically redirect to https for the
"available_apps" call. This is a anonymous call so it could be served via http too.

mvo@bod:~/devel/software-center/trunk$ SOFTWARE_CENTER_DEBUG_HTTP=1 PYTHONPATH=. utils/piston-helpers/piston_generic_helper.py --output=text --debug SoftwareCenterAgentAPI available_apps '{ "lang" : "en", "series" : "oneiric", "arch" : "i386" }' 2>/dev/null
connect: (software-center.ubuntu.com, 80)
send: u'GET /api/2.0/applications/en/ubuntu/oneiric/i386/ HTTP/1.1\r\nHost: software-center.ubuntu.com\r\naccept-encoding: gzip, deflate\r\nuser-agent: Python-httplib2/0.7.0 (gzip)\r\n\r\n'
reply: 'HTTP/1.1 301 Moved Permanently\r\n'
header: Date: Tue, 31 Jan 2012 08:26:44 GMT
header: Server: Apache/2.2.14 (Ubuntu)
header: Location: https://software-center.ubuntu.com/api/2.0/applications/en/ubuntu/oneiric/i386/
header: Vary: Accept-Encoding
header: Content-Encoding: gzip
header: Content-Length: 278
header: Connection: close
header: Content-Type: text/html; charset=iso-8859-1
connect: (software-center.ubuntu.com, 443)
send: 'GET /api/2.0/applications/en/ubuntu/oneiric/i386/ HTTP/1.1\r\nHost: software-center.ubuntu.com\r\naccept-encoding: gzip, deflate\r\nuser-agent: Python-httplib2/0.7.0 (gzip)\r\n\r\n'
reply: 'HTTP/1.1 200 OK\r\n'
header: Date: Tue, 31 Jan 2012 08:26:45 GMT
header: Server: Apache/2.2.14 (Ubuntu)
header: Expires: Tue, 31 Jan 2012 08:34:33 GMT
header: Vary: Authorization
header: ETag: "566fc18647ab384200ba799fcee5c360"
header: Cache-Control: max-age=600
header: Last-Modified: Tue, 31 Jan 2012 08:24:33 GMT
header: Content-Type: application/json; charset=utf-8
header: Via: 1.1 software-center.ubuntu.com
header: Transfer-Encoding: chunked