Use cliff.lister for tempest workspace command

This commit makes tempest workspace command use cliff.lister to show
various formats. And this commit splits the original class -
TempestWorkspace into the subcommand classes to use the cliff.lister
class. With this splitting, we can get the subcommand helps as a side
effect.

Change-Id: I07c69c467743a2f132c99d992773a53bda3bec7b
diff --git a/setup.cfg b/setup.cfg
index b2035bc..b292970 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -39,7 +39,11 @@
     cleanup = tempest.cmd.cleanup:TempestCleanup
     list-plugins = tempest.cmd.list_plugins:TempestListPlugins
     verify-config = tempest.cmd.verify_tempest_config:TempestVerifyConfig
-    workspace = tempest.cmd.workspace:TempestWorkspace
+    workspace_register = tempest.cmd.workspace:TempestWorkspaceRegister
+    workspace_rename = tempest.cmd.workspace:TempestWorkspaceRename
+    workspace_move = tempest.cmd.workspace:TempestWorkspaceMove
+    workspace_remove = tempest.cmd.workspace:TempestWorkspaceRemove
+    workspace_list = tempest.cmd.workspace:TempestWorkspaceList
     run = tempest.cmd.run:TempestRun
 oslo.config.opts =
     tempest.config = tempest.config:list_opts