Migrated microversion testing framework to tempest/lib

Tempest implements the microversion testing support and
that framework and interfaces have been tested by implementing
the Compute 2.2 microversion as well as by their unit tests.

Those should be stable interfaces so that can be consumed by other
projects microversion testing either in tempest or outside tempest.

To make them as stable interface, this commit moving that framework and
its interfaces to tempest/lib folder.

Adding release notes and library doc for those interface.

Partially implements blueprint api-microversions-testing-support

Change-Id: Icbdcfb4cd5b7fb1029eec035b9e0024be59c8d1f
diff --git a/tempest/tests/test_microversions.py b/tempest/tests/test_microversions.py
index 6738641..f19ee49 100644
--- a/tempest/tests/test_microversions.py
+++ b/tempest/tests/test_microversions.py
@@ -17,7 +17,7 @@
 
 from tempest.api.compute import base as compute_base
 from tempest import config
-from tempest import exceptions
+from tempest.lib import exceptions
 from tempest.tests import base
 from tempest.tests import fake_config