feature: Added '--specignore' option to pass file containing specs to be ignored for fission spec commands (#2239)

- New flag `--specignore` has been added for command fission spec [list | validate | apply | destroy]
- This flag is optional.
- The default spec ignore file name is `.specignore`, if the flag is not used
- The spec ignore file existence will be checked in the `--specdir` path
- If spec ignore file is passed to the flag, with a name other than .specignore and if it does not exist in the `--specdir` path then an error will be returned.
- `--specdir` will be the root path against which the patterns will be evaluated
- The behaviour of the spec ignore file will be similar to .gitignore (only for yml and yaml files). For reference: http://git-scm.com/docs/gitignore

pkg/fission-cli/cmd/spec/spec.go

@@ -171,7 +171,7 @@ func SpecSave(resource interface{}, specFile string) error {
 		return err
 	}
 
-	fr, err := ReadSpecs(specDir)
+	fr, err := ReadSpecs(specDir, util.SPEC_IGNORE_FILE)
 	if err != nil {
 		return errors.Wrap(err, fmt.Sprintf("error reading spec in '%v'", specDir))
 	}