Fix URLs to use v3 when only v2 endpoint is listed in the catalog

[achevalet]

It covers the cases where we can authenticate with keystone v3 but the endpoint returned in the catalog is v2
see #492

You guys can probably do something much cleaner as I have poor ruby skills, but it fixes my issue and the tests passed so I'm proposing.. :-)

[theopenlab-ci]

Build succeeded.

• fog-openstack-unittest-test : SUCCESS in 14m 24s
• fog-openstack-unittest-spec : SUCCESS in 15m 46s

[theopenlab-ci]

Build failed.

• fog-openstack-unittest-test : SUCCESS in 14m 09s
• fog-openstack-unittest-spec : FAILURE in 5m 34s

[theopenlab-ci]

Build succeeded.

• fog-openstack-unittest-test : SUCCESS in 12m 49s
• fog-openstack-unittest-spec : SUCCESS in 14m 50s

[theopenlab-ci]

Build succeeded.

• fog-openstack-unittest-test : SUCCESS in 14m 50s
• fog-openstack-unittest-spec : SUCCESS in 11m 47s

[pdion891]

tested on an OpenStack not exposing a endpoint for v3 and this fix work fine.

[ShamoX]

Just have a little problem with that, it's missing tests implementation of the corrected bug.

I can believe @pdion891 on word but it seems a little risky for the others.

Implemented tests are passing anyway.

[ares]

A test would certainly be good, @achevalet please let us know if you plan to add one.

[pdion891]

Just have a little problem with that, it's missing tests implementation of the corrected bug.

I can believe @pdion891 on word but it seems a little risky for the others.

Implemented tests are passing anyway.

For sure I've only validated the use case that was valid on my side where the /v3 is not exposed.

[achevalet]

Quite busy, I would be grateful if someone can contribute here