Feature 10950 Replace pycrypto with pycryptodome

Remove the pycrypto library and change encrypt and decrypt methods to work with pycryptodome.
Move encryption methods from N2VC to common.

Change-Id: I12a5f6138664ab6ebb7100c82523e91750f05f14
Signed-off-by: Gulsum Atici <gulsum.atici@canonical.com>
diff --git a/osm_common/fsmongo.py b/osm_common/fsmongo.py
index 727410e..f99267f 100644
--- a/osm_common/fsmongo.py
+++ b/osm_common/fsmongo.py
@@ -570,9 +570,7 @@
         self.__update_local_fs(from_path=from_path)
 
     def _update_mongo_fs(self, from_path):
-
         os_path = self.path + from_path
-
         # Obtain list of files and dirs in filesystem
         members = []
         for root, dirs, files in os.walk(os_path):
@@ -615,7 +613,6 @@
             remote_files.pop(rel_filename, None)
 
             if last_modified_date >= upload_date:
-
                 stream = None
                 fh = None
                 try:
@@ -646,13 +643,12 @@
                     if stream:
                         stream.close()
 
-        # delete files that are not any more in local fs
+        # delete files that are not anymore in local fs
         for remote_file in remote_files.values():
             for file in remote_file:
                 self.fs.delete(file._id)
 
     def _get_mongo_files(self, from_path=None):
-
         file_dict = {}
         file_cursor = self.fs.find(no_cursor_timeout=True, sort=[("uploadDate", -1)])
         for file in file_cursor: