Fix remote settings overwrite at startup

Mycroft always mangeled any local settings changes at startup.

This caches the last settings from home on disk and only updates skills
if there is a change.

This means that as if a member is changed locally (manually edited or
changed by the skill itself) it will be kept until another change is made
to the skill on Home.

mycroft/skills/settings.py

@@ -57,9 +57,11 @@
 """
 import json
 import os
+from os.path import dirname
 import re
 from pathlib import Path
 from threading import Timer
+from xdg.BaseDirectory import xdg_cache_home
 
 import yaml
 
@@ -68,6 +70,7 @@
 from mycroft.messagebus.message import Message
 from mycroft.util import camel_case_split
 from mycroft.util.log import LOG
+from mycroft.util.file_utils import ensure_directory_exists
 from .msm_wrapper import build_msm_config, create_msm
 
 ONE_MINUTE = 60
@@ -309,6 +312,42 @@ def _issue_api_call(self):
         return success
 
 
+# Path to remote cache
+REMOTE_CACHE = Path(xdg_cache_home, 'mycroft', 'remote_skill_settings.json')
+
+
+def load_remote_settings_cache():
+    """Load cached remote skill settings.
+
+    Returns:
+        (dict) Loaded remote settings cache or None of none exists.
+    """
+    remote_settings = None
+    if REMOTE_CACHE.exists():
+        try:
+            with open(str(REMOTE_CACHE)) as cache:
+                remote_settings = json.load(cache)
+        except Exception as error:
+            LOG.warning('Failed to read remote_cache ({})'.format(error))
+    return remote_settings
+
+
+def save_remote_settings_cache(remote_settings):
+    """Save updated remote settings to cache file.
+
+    Arguments:
+        remote_settings (dict): downloaded remote settings.
+    """
+    try:
+        ensure_directory_exists(dirname(str(REMOTE_CACHE)))
+        with open(str(REMOTE_CACHE), 'w') as cache:
+            json.dump(remote_settings, cache)
+    except Exception as error:
+        LOG.warning('Failed to write remote_cache. ({})'.format(error))
+    else:
+        LOG.debug('Updated local cache of remote skill settings.')
+
+
 class SkillSettingsDownloader:
     """Manages download of skill settings.
 
@@ -319,8 +358,8 @@ class SkillSettingsDownloader:
     def __init__(self, bus):
         self.bus = bus
         self.continue_downloading = True
-        self.last_download_result = {}
-        self.remote_settings = None
+        self.last_download_result = load_remote_settings_cache()
+
         self.api = DeviceApi()
         self.download_timer = None
         self.sync_enabled = Configuration.get()["server"]\
@@ -351,11 +390,11 @@ def download(self, message=None):
                     LOG.debug('Skill settings changed since last download')
                     self._emit_settings_change_events(remote_settings)
                     self.last_download_result = remote_settings
+                    save_remote_settings_cache(remote_settings)
                 else:
                     LOG.debug('No skill settings changes since last download')
         else:
             LOG.debug('Settings not downloaded - device is not paired')
-
         # If this method is called outside of the timer loop, ensure the
         # existing timer is canceled before starting a new one.
         if self.download_timer: