Handle duplicate archive and package specs; handle multifile archives better (#1018)

Archives with multiple files should have all files in the inputs.
Also clean up some inconsistent variable naming -- archive name,
archive file path, and archive input files were all stored in
incorrectly-named variables.

fission/upgrade.go

@@ -293,7 +293,7 @@ func upgradeRestoreState(c *cli.Context) error {
 		tmpfile.Close()
 
 		// upload
-		archive := createArchive(client, tmpfile.Name(), "")
+		archive := uploadArchive(client, tmpfile.Name())
 		os.Remove(tmpfile.Name())
 
 		// create pkg