cli/command/plugin: fix linting issues, and assorted cleanups

- fix various unhandled errors
- remove some locally defined option-types in favor of option-types
  defined by the client / api
- don't use unkeyed structs in tests, and add docs for some subtests
- fix some values in tests that triggered "spellcheck" warnings
- inline vars / functions that only had a single use.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/plugin/create.go

@@ -40,7 +40,7 @@ func validateConfig(path string) error {
 	return err
 }
 
-// validateContextDir validates the given dir and returns abs path on success.
+// validateContextDir validates the given dir and returns its absolute path on success.
 func validateContextDir(contextDir string) (string, error) {
 	absContextDir, err := filepath.Abs(contextDir)
 	if err != nil {