Make adjstments for btrfs-progs-4.4

With btrfs-progs 4.4.1 the format of two messages was changed, causing us to fail to find the a btrfs root directory as well as a test failure due to a string mismatch. This change addresses both problems. Note that we do not keep backwards compatibility for we do not have paths accepting the previous strings, meaning that btrfs-progs version 4.4 (or higher) is a requirement.

Author: d-e-s-o

btrfs-backup/src/deso/btrfs/repository.py

@@ -99,7 +99,7 @@
 # given directory is a subvolume. However, if it is the root of the
 # btrfs file system then it will end in 'is btrfs root'. We need to
 # detect this case to determine the btrfs root.
-_SHOW_IS_ROOT = "is btrfs root"
+_SHOW_IS_ROOT = "is toplevel subvolume"
 _SHOW_SUBVOL_NAME_REGEX = regex(r"\s*Name:\s*(.*)")
 # The marker ending the file list reported by the diff() function. If
 # this marker is the only thing reported then no files have changed.

btrfs-backup/src/deso/btrfs/test/testRepository.py

@@ -473,7 +473,7 @@ def testRepositorySyncFailsForNonExistentSubvolume(self):
  backup = make(m, "backup")
 
  directory = "non-existent-directory"
- regex = r"error accessing.*%s" % directory
+ regex = r"cannot access subvolume.*%s" % directory
  src = Repository(snaps)
  dst = Repository(backup)