Fix migration crashes.

selfprivacy_api/migrations/__init__.py

@@ -20,4 +20,9 @@ def run_migrations():
     for migration in migrations:
         if migration.get_migration_name() not in skipped_migrations:
             if migration.is_migration_needed():
+                try:
                     migration.migrate()
+                except Exception as e:
+                    print(f"Error while migrating {migration.get_migration_name()}")
+                    print(e)
+                    print("Skipping this migration")

selfprivacy_api/migrations/fix_nixos_config_branch.py

@@ -17,13 +17,20 @@ class FixNixosConfigBranch(Migration):
 
     def is_migration_needed(self):
         """Check the current branch of /etc/nixos and return True if it is rolling-testing"""
+        current_working_directory = os.getcwd()
+        try:
+            os.chdir("/etc/nixos")
             nixos_config_branch = subprocess.check_output(
                 ["git", "rev-parse", "--abbrev-ref", "HEAD"], start_new_session=True
             )
+            os.chdir(current_working_directory)
             if nixos_config_branch.decode("utf-8").strip() == "rolling-testing":
                 return True
             else:
                 return False
+        except subprocess.CalledProcessError:
+            os.chdir(current_working_directory)
+            return False
 
     def migrate(self):
         """Affected server pulled the config with the --single-branch flag.
@@ -32,6 +39,7 @@ class FixNixosConfigBranch(Migration):
         """
         print("Fixing Nixos config branch")
         current_working_directory = os.getcwd()
+        try:
             os.chdir("/etc/nixos")
 
             subprocess.check_output(
@@ -45,6 +53,9 @@ class FixNixosConfigBranch(Migration):
             subprocess.check_output(["git", "fetch", "--all"])
             subprocess.check_output(["git", "pull"])
             subprocess.check_output(["git", "checkout", "master"])
-
             os.chdir(current_working_directory)
             print("Done")
+        except subprocess.CalledProcessError:
+            os.chdir(current_working_directory)
+            print("Error")
+