fixed test connection for existing compute-resource.
added blank option in ovirt select template.
Do not block create and destroy volume if api version is 3.1 or later.
fixes #2224 Selecting a RHEV 3.1 template does not work properly
fixes #2163 New host installation fails with RHEV 3.1
fixes #2242 - concatenate HTML errors, don't use Array#to_s on Ruby 1.9