Allow u-* properties to be invalid URIs

Parsing u-* properties as URIs is causing spec failures here because SSH clone urls are used. https://github.com/G5/g5_sibling_deployer_engine/pull/8

    URI::InvalidURIError:
       bad URI(is not URI?): git@github.com:g5search/g5-client-hub-deployer.git
     # ./app/models/sibling.rb:19:in `main_app_hcard'

This PR rescues the error. It also rescues `URI::BadURIError` which happens if the base url is not absolute.