Name backup directories with 'before-upgrade'

Closes gh-2811

docs/usage/upgrade.rst

@@ -6,7 +6,7 @@ Examples
 
     # Upgrade the borg repository to the most recent version.
     $ borg upgrade -v /path/to/repo
-    making a hardlink copy in /path/to/repo.upgrade-2016-02-15-20:51:55
+    making a hardlink copy in /path/to/repo.before-upgrade-2016-02-15-20:51:55
     opening attic repository with borg and converting
     no key file found for repository
     converting repo index /path/to/repo/index.0

docs/usage/upgrade.rst.inc

@@ -134,7 +134,7 @@ make sure the cache files are also removed:
 
 Unless ``--inplace`` is specified, the upgrade process first
 creates a backup copy of the repository, in
-REPOSITORY.upgrade-DATETIME, using hardlinks. This takes
+REPOSITORY.before-upgrade-DATETIME, using hardlinks. This takes
 longer than in place upgrades, but is much safer and gives
 progress information (as opposed to ``cp -al``). Once you are
 satisfied with the conversion, you can safely destroy the
@@ -144,4 +144,4 @@ WARNING: Running the upgrade in place will make the current
 copy unusable with older version, with no way of going back
 to previous versions. This can PERMANENTLY DAMAGE YOUR
 REPOSITORY!  Attic CAN NOT READ BORG REPOSITORIES, as the
-magic strings have changed. You have been warned.
+magic strings have changed. You have been warned.

src/borg/archiver.py

@@ -3391,7 +3391,7 @@ class Archiver:
 
         Unless ``--inplace`` is specified, the upgrade process first
         creates a backup copy of the repository, in
-        REPOSITORY.upgrade-DATETIME, using hardlinks. This takes
+        REPOSITORY.before-upgrade-DATETIME, using hardlinks. This takes
         longer than in place upgrades, but is much safer and gives
         progress information (as opposed to ``cp -al``). Once you are
         satisfied with the conversion, you can safely destroy the

src/borg/upgrader.py

@@ -35,7 +35,7 @@ class AtticRepositoryUpgrader(Repository):
         with self:
             backup = None
             if not inplace:
-                backup = '{}.upgrade-{:%Y-%m-%d-%H:%M:%S}'.format(self.path, datetime.datetime.now())
+                backup = '{}.before-upgrade-{:%Y-%m-%d-%H:%M:%S}'.format(self.path, datetime.datetime.now())
                 logger.info('making a hardlink copy in %s', backup)
                 if not dryrun:
                     shutil.copytree(self.path, backup, copy_function=os.link)