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 @@ SkillSettings Usage Example:
 """
 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.configuration import Configuration
 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 @@ class SettingsMetaUploader:
         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 = {}
+    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 @@ class SkillSettingsDownloader:
                     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: