flag for output json or yaml added in install.go, repo_list.go, search.go,...

flag for output json or yaml added in install.go, repo_list.go, search.go, status.go and upgrade.go.
unit test adapted for output json or yaml in install_test.go and search_test.go.
docs modified for new flag helm_install.md, helm_repo_list.md, helm_search.md and helm_upgrade.md

Signed-off-by: Michael Schaefer <michael.schaefer@sew-eurodrive.de>