Add sysupgrade state file

When IPA package is being updated, some of the configuration files
are also updated. Sometimes it may be useful to store upgrade meta
information for next package upgrades. For example an information
that some config file was already updated and we don't want to
update it again if user purposedly reverted the change.

This patch adds a new StateFile in /var/lib/ipa/sysupgrade which
is capable of holding this information. New sysupgrade.py module
was created to provide simple API to access the upgrade state
information.

ipapython/sysrestore.py

@@ -41,7 +41,7 @@ SYSRESTORE_STATEFILE = "sysrestore.state"
 class FileStore:
     """Class for handling backup and restore of files"""
 
-    def __init__(self, path = SYSRESTORE_PATH):
+    def __init__(self, path = SYSRESTORE_PATH, index_file = SYSRESTORE_INDEXFILE):
         """Create a _StoreFiles object, that uses @path as the
         base directory.
 
@@ -49,7 +49,7 @@ class FileStore:
         about the original location of the saved files.
         """
         self._path = path
-        self._index = self._path + "/" + SYSRESTORE_INDEXFILE
+        self._index = os.path.join(self._path, index_file)
 
         self.random = random.Random()
 
@@ -279,7 +279,7 @@ class StateFile:
     enabled=False
     """
 
-    def __init__(self, path = SYSRESTORE_PATH):
+    def __init__(self, path = SYSRESTORE_PATH, state_file = SYSRESTORE_STATEFILE):
         """Create a StateFile object, loading from @path.
 
         The dictionary @modules, a member of the returned object,
@@ -290,7 +290,7 @@ class StateFile:
         The keys in these latter dictionaries are arbitrary strings
         and the values may either be strings or booleans.
         """
-        self._path = path+"/"+SYSRESTORE_STATEFILE
+        self._path = os.path.join(path, state_file)
 
         self.modules = {}
 
@@ -359,6 +359,31 @@ class StateFile:
 
         self.save()
 
+    def get_state(self, module, key):
+        """Return the value of an item of system state from @module,
+        identified by the string @key.
+
+        If the item doesn't exist, #None will be returned, otherwise
+        the original string or boolean value is returned.
+        """
+        if not self.modules.has_key(module):
+            return None
+
+        return self.modules[module].get(key, None)
+
+    def delete_state(self, module, key):
+        """Delete system state from @module, identified by the string
+        @key.
+
+        If the item doesn't exist, no change is done.
+        """
+        try:
+            del self.modules[module][key]
+        except KeyError:
+            pass
+        else:
+            self.save()
+
     def restore_state(self, module, key):
         """Return the value of an item of system state from @module,
         identified by the string @key, and remove it from the backed
@@ -368,16 +393,10 @@ class StateFile:
         the original string or boolean value is returned.
         """
 
-        if not self.modules.has_key(module):
-            return None
+        value = self.get_state(module, key)
 
-        if not self.modules[module].has_key(key):
-            return None
-
-        value = self.modules[module][key]
-        del self.modules[module][key]
-
-        self.save()
+        if value is not None:
+            self.delete_state(module, key)
 
         return value