Fix automated rb-site installs with support-related defaults.

When running `rb-site install` in an automated mode (using --noinput),
things would fail if either --company or --admin-email were left out.
We were saving the default values of None, but the support data
generation couldn't serialize these to strings.

To get around this, some people tried posting empty strings (using "" or
'""').

We now normalize None or single/double quotes to an actual empty string.

Fixes bug #3544
Reviewed at https://reviews.reviewboard.org/r/6274/
Merge branch 'release-2.0.x'