Add --archive.tar.binary parameter (#286)

* Add --archive.tar.binary parameter

Allows specifying a custom location of the "tar" command to use.
Also, the flags sent to "tar" are sent individually (`tar -cf` becomes `tar -c -f`).

This allows easily customizing how the archiving is performed without having to add
lots of new options. For example, you could encrypt backup data via a simple shell script
and specify it for --archive.tar.binary:

```
#!/bin/bash
gpg_pubkey_id=XXXXXXX
new_args=""

while [ "${#}" -gt 0 ]; do
  case "$1" in
    -f)
      shift;
      original_output_file="${1}"
      shift
      new_args="${new_args} --to-stdout"
      ;;
    *)
      new_args="${new_args} ${1}"
      shift
      ;;
  esac
done

tar ${new_args} | gpg --always-trust --encrypt --recipient ${gpg_pubkey_id} -z 0 --output ${original_output_file}
```

This has several advantages:

* Backups are never written to disk unencrypted
* Encryption can be done in one go, instead of causing the potentially heavy additional
  I/O a separate encryption step would incur.
* It's transparent for the upload stages, so you can still benefit from the integrated
  S3 (or other) uploads.

* Related: Fix flake8: Make regex a raw string

Author: dschneller

mongodb_consistent_backup/Archive/Tar/Tar.py

@@ -26,7 +26,7 @@ class Tar(Task):
     def __init__(self, manager, config, timer, base_dir, backup_dir, **kwargs):
         super(Tar, self).__init__(self.__class__.__name__, manager, config, timer, base_dir, backup_dir, **kwargs)
         self.compression_method = self.config.archive.tar.compression
-        self.binary             = "tar"
+        self.binary             = self.config.archive.tar.binary
 
         self._pool   = None
         self._pooled = []

mongodb_consistent_backup/Archive/Tar/TarThread.py

@@ -32,12 +32,13 @@ def run(self):
                     backup_base_name = os.path.basename(self.backup_dir)
 
                     log_msg   = "Archiving directory: %s" % self.backup_dir
-                    cmd_flags = ["-C", backup_base_dir, "-cf", self.output_file, "--remove-files", backup_base_name]
+                    cmd_flags = ["-C", backup_base_dir, "-c", "-f", self.output_file, "--remove-files"]
 
                     if self.do_gzip():
-                        log_msg   = "Archiving and compressing directory: %s" % self.backup_dir
-                        cmd_flags = ["-C", backup_base_dir, "-czf", self.output_file, "--remove-files", backup_base_name]
+                        log_msg = "Archiving and compressing directory: %s" % self.backup_dir
+                        cmd_flags.append("-z")
 
+                    cmd_flags.append(backup_base_name)
                     logging.info(log_msg)
                     self.running  = True
                     self._command = LocalCommand(self.binary, cmd_flags, self.verbose)

mongodb_consistent_backup/Archive/Tar/__init__.py

@@ -2,6 +2,8 @@
 
 
 def config(parser):
+    parser.add_argument("--archive.tar.binary", dest="archive.tar.binary", default='tar', type=str,
+                        help="Path to tar binary (default: tar)")
     parser.add_argument("--archive.tar.compression", dest="archive.tar.compression",
                         help="Tar archiver compression method (default: gzip)", default='gzip', choices=['gzip', 'none'])
     parser.add_argument("--archive.tar.threads", dest="archive.tar.threads",