Fix to show cli subcommand help message
Fix to show cli subcommand help message

This commit fixes to show help messages of Tempest cli subcommands with
'-h/--help' option such as 'tempest complete -h'.

NOTE:
'deferred_help' param is for allowing deferring help print after
initialize_app originally. But we can see the subcommand help messages
with setting True to deferred_help now[1].

[1] I628bbfc383de516045288512cc023213d723a027

Closes-Bug: #1533448
Change-Id: Ia4ffcbd4f7db2d945098a40bb7c3d2fbb1b2a64b

sebrandon1/tempest,vedujoshi/tempest,vedujoshi/tempest,sebrandon1/tempest,zsoltdudas/lis-tempest,masayukig/tempest,openstack/tempest,Tesora/tesora-tempest,Juniper/tempest,openstack/tempest,LIS/lis-tempest,LIS/lis-tempest,Tesora/tesora-tempest,zsoltdudas/lis-tempest,cisco-openstack/tempest,cisco-openstack/tempest,Juniper/tempest,bigswitch/tempest,masayukig/tempest,bigswitch/tempest