decode mb/xb version from byte literal

For mariabackup and xtrabackup plugins, correct cosmetic issue shown here:

Executing: /bin/mariabackup --version
b'/bin/mariabackup based on MariaDB server 10.11.7-MariaDB Linux (x86_64)'

Proposed:

@@ -72,7 +72,7 @@
         raise BackupError("Failed to run %s: [%d] %s" % cmdline, exc.errno, exc.strerror)

     for line in process.stdout:
-        LOG.info("# %s", line.decode("UTF-8").rstrip())
+        LOG.info("%s", line.rstrip())
     process.wait()
     if process.returncode != 0:
         raise BackupError("%s returned failure status [%d]" % (cmdline, process.returncode))

holland-backup / holland

decode mb/xb version from byte literal #363