The previous behavior in keystoneauth for constructing an unversioned
endpoint if there's a versioned endpoint in the catalog would result in
a trailing slash. Ensure that we end up with trailing slashses on
endpoints we construct.
On the other hand, do not add trailing slashes to urls we're actually
using. If someone wants a / the url they register with the catalog, they
can put one there.
Change-Id: I2798216b5b93d49fd5d3d865193cc0be6a1f6f0d
Closes-Bug: #1705770
ccbd20ed9c