tests: fix minor bugs
tests: fix minor bugs

- `helm_read` is not a command, but a variable
- If `helm` was installed in `helm.sh up`, the following `heml.sh clean`
  fails since `helm_rest` can't find the installed `helm`.

Signed-off-by: Satoru Takeuchi <0be322b419f8cd46ee75447832ef0476dff222bc@gmail.com>

rook/nfs,rook/nfs,rook/rook,rook/rook,rook/nfs,rook/rook,rook/rook,rook/rook