Make CLI functions return error instead of fatal out (#1379)

Before this PR, CLI functions fatal out when encountering error
instead of returning it. Such behavior makes it hard to reuse 
the functions nor writing unit tests. This PR aims to make functions 
return errors instead of error out.

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

@@ -61,7 +61,7 @@ func CreateArchive(client *client.Client, includeFiles []string, noZip bool, kee
 		// Get files from inputs as number of files decide next steps
 		files, err := utils.FindAllGlobs([]string{path})
 		if err != nil {
-			util.CheckErr(err, "finding all globs")
+			return nil, errors.Wrap(err, "error finding all globs")
 		}
 
 		if len(files) == 0 {
@@ -90,14 +90,18 @@ func CreateArchive(client *client.Client, includeFiles []string, noZip bool, kee
 
 			// check if this AUS exists in the specs; if so, don't create a new one
 			fr, err := spec.ReadSpecs(specDir)
-			util.CheckErr(err, "read specs")
+			if err != nil {
+				return nil, errors.Wrap(err, "error reading specs")
+			}
 			if m := fr.SpecExists(aus, false, true); m != nil {
 				fmt.Printf("Re-using previously created archive %v\n", m.Name)
 				aus.Name = m.Name
 			} else {
 				// save the uploadspec
 				err := spec.SpecSave(*aus, specFile)
-				util.CheckErr(err, fmt.Sprintf("write spec file %v", specFile))
+				if err != nil {
+					return nil, errors.Wrapf(err, "write spec file %v", specFile)
+				}
 			}
 
 			// create the archive object
@@ -118,11 +122,18 @@ func CreateArchive(client *client.Client, includeFiles []string, noZip bool, kee
 			}, nil
 		}
 		// download the file before we archive it
-		dst := pkgutil.DownloadToTempFile(fileURL)
+		dst, err := pkgutil.DownloadToTempFile(fileURL)
+		if err != nil {
+			return nil, err
+		}
 		includeFiles = []string{dst}
 	}
 
-	archivePath := makeArchiveFile("", includeFiles, noZip)
+	archivePath, err := makeArchiveFile("", includeFiles, noZip)
+	if err != nil {
+		return nil, err
+	}
+
 	ctx := context.Background()
 	return pkgutil.UploadArchiveFile(ctx, client, archivePath)
 }
@@ -134,7 +145,7 @@ func CreateArchive(client *client.Client, includeFiles []string, noZip bool, kee
 // returned as-is with no zipping.  (This is used for compatibility
 // with v1 envs.)  noZip is IGNORED if there is more than one input
 // file.
-func makeArchiveFile(archiveNameHint string, archiveInput []string, noZip bool) string {
+func makeArchiveFile(archiveNameHint string, archiveInput []string, noZip bool) (string, error) {
 
 	// Unique name for the archive
 	archiveName := archiveName(archiveNameHint, archiveInput)
@@ -142,34 +153,34 @@ func makeArchiveFile(archiveNameHint string, archiveInput []string, noZip bool)
 	// Get files from inputs as number of files decide next steps
 	files, err := utils.FindAllGlobs(archiveInput)
 	if err != nil {
-		util.CheckErr(err, "finding all globs")
+		return "", errors.Wrap(err, "error finding all globs")
 	}
 
 	// We have one file; if it's a zip file, no need to archive it
 	if len(files) == 1 {
 		// make sure it exists
 		if _, err := os.Stat(files[0]); err != nil {
-			util.CheckErr(err, fmt.Sprintf("open input file %v", files[0]))
+			return "", errors.Wrapf(err, "open input file %v", files[0])
 		}
 
 		// if it's an existing zip file OR we're not supposed to zip it, don't do anything
 		if archiver.Zip.Match(files[0]) || noZip {
-			return files[0]
+			return files[0], nil
 		}
 	}
 
 	// For anything else, create a new archive
 	tmpDir, err := utils.GetTempDir()
 	if err != nil {
-		util.CheckErr(err, "create temporary archive directory")
+		return "", errors.Wrap(err, "error create temporary archive directory")
 	}
 
 	archivePath, err := utils.MakeZipArchive(filepath.Join(tmpDir, archiveName), archiveInput...)
 	if err != nil {
-		util.CheckErr(err, "create archive file")
+		return "", errors.Wrap(err, "create archive file")
 	}
 
-	return archivePath
+	return archivePath, nil
 }
 
 // Name an archive