skaffold inspect command does not show all supported flags for its subcommands

Currently if you attempt to list flags for `skaffold inspect`, the inherited flags from the root command are not shown. UX-wise I believe this is confusing as it would be hard to find all of the supported flags for the command. Below is an example showing this:
```
aprindle@aprindle ~/skaffold [inspect-tests-add-test-type]$ skaff inspect build-env list --help
Print the list of active build environments.

Examples:
# Get list of target build environments with activated profiles p1 and p2
skaffold inspect build-env list -p p1,p2 --format json

Options:
-p, --profile=[]: Profile names to activate

Usage:
skaffold inspect build-env list [flags] [options]

Use "skaffold options" for a list of global command-line options (applies to all commands).
```

```
aprindle@aprindle ~/skaffold [inspect-tests-add-test-type]$ skaffold inspect --help
Helper commands for Cloud Code IDEs to interact with and modify skaffold configuration files.

Available Commands:
build-env Interact with skaffold build environment definitions.
modules Interact with configuration modules
profiles Interact with configuration profiles

Use "skaffold --help" for more information about a given command.
```