github.com/juju/juju/environs unit tests fail if xenial is the LTS

The following tests fail for this pacakge when xenial is the default lts (from distro-info --lts):

FAIL: open_test.go:47: OpenSuite.TestNewDummyEnviron

[LOG] 0:00.005 DEBUG juju.environs.tools reading v1.* tools
[LOG] 0:00.005 INFO juju.environs.testing uploading FAKE tools 1.99.0-precise-amd64
[LOG] 0:00.007 INFO juju.environs.testing uploading FAKE tools 1.99.0-trusty-amd64
[LOG] 0:00.009 INFO juju.environs.testing uploading FAKE tools 1.99.0-wily-amd64
[LOG] 0:00.021 INFO juju.environs.tools Writing tools/streams/v1/index2.json
[LOG] 0:00.021 INFO juju.environs.tools Writing tools/streams/v1/index.json
[LOG] 0:00.021 INFO juju.environs.tools Writing tools/streams/v1/com.ubuntu.juju-released-tools.json
[LOG] 0:00.034 INFO juju.network setting prefer-ipv6 to false
[LOG] 0:00.034 DEBUG juju.environs.bootstrap model "only" supports service/machine networks: true
[LOG] 0:00.034 DEBUG juju.environs.bootstrap network management by juju enabled: true
[LOG] 0:00.034 INFO juju.environs.bootstrap looking for bootstrap tools: version=<nil>
[LOG] 0:00.034 INFO juju.environs.tools finding tools in stream "released"
[LOG] 0:00.034 INFO juju.environs.tools reading tools with major.minor version 1.99
open_test.go:67:
    c.Assert(err, jc.ErrorIsNil)
... value *errors.Err = &errors.Err{message:"no matching tools available", cause:error(nil), previous:error(nil), file:"github.com/juju/juju/tools/list.go", line:19} ("no matching tools available")
... error stack:
 github.com/juju/juju/tools/list.go:19: no matching tools available