Fix SVN auth/HTTPS support with Subvertpy.
Fix SVN auth/HTTPS support with Subvertpy.

When using Subvertpy as an SCM backend, adding an HTTPS repository
requiring Basic authentication would fail showing:
A repository was not found at the specified path.

Weirdly, when passing the `subvertpy.AUTH_PARAM_DEFAULT_*` constants to
`subvertpy.ra.Auth.auth.set_parameter()` instead of the corresponding
strings, it works.
Also, in `accept_ssl_certificate()` username/password were not passed.

Testing Done:
* Created Docker container from easybe/alpine-reviewboard:wip
* Sucessfully added an SVN repository requiring HTTPS and Basic auth

Reviewed at https://reviews.reviewboard.org/r/10037/

chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard