refactor(remote-backup.sh): set pipefail option and add more comments.

We don't use pipefail here and it was added for consistency and for future.

No functional changes.

Author: php-coder

vagrant/provisioning/roles/mystamps-backup/templates/remote-backup.sh

@@ -1,8 +1,15 @@
 #!/bin/bash
 
+# Treat unset variables and parameters as an error when performing parameter expansion
 set -o nounset
+
+# Exit immediately if command returns a non-zero status
 set -o errexit
 
+# Return value of a pipeline is the value of the last command to exit with a non-zero status
+set -o pipefail
+
+
 UPLOADS_DST='{{ uploads_target_url }}'
 MYSQL_BACKUPS_DST='{{ mysql_backups_target_url }}'
 PASSPHRASE='{{ gpg_passphrase }}'