CLOUDSTACK-6695: Added support to the UI for uploading a chain of certificates

In the "SSL Certificate" dialog we added:
- new field for the root certificate;
- a button to add intermediate certificates if necessary; when this is pressed, a new field, called "Intermediate certificate 1" is added; pressed again, "Intermediate certificate 2" field is added, and so on.

We upload the certificates in order: first the root certificate (with id=1), then the intermediate certificates (with id=2,3,..) and finally the server certificate.
When uploading a certificate, we wait for the upload to be completed successfully and only then we proceed to uploading the next one. If one fails, we report failure and don't continue with the remaining.

Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>