Add ability to invalidate caches

For efficiency, rtslib may have caches (today for the data
in configfs).  A client may need to clear out these caches
such as via the refresh option in targetcli.

* Add new invalidate_caches method to RTSRoot.  While this only
has a single cache today, it gives the ability to extend to
any future caches.
* While bs_cache really should be private, it probably
shouldn't be changed given that this is a library and may be
used elsewhere.

Signed-off-by: Amartey Pearson <apearson@us.ibm.com>

rtslib/root.py

@@ -25,7 +25,7 @@
 from .node import CFSNode
 from .target import Target
 from .fabric import FabricModule
-from .tcm import so_mapping, StorageObject
+from .tcm import so_mapping, bs_cache, StorageObject
 from .utils import RTSLibError, RTSLibALUANotSupported, modprobe, mount_configfs
 from .utils import dict_remove, set_attributes
 from .alua import ALUATargetPortGroup
@@ -290,6 +290,12 @@ def restore_from_file(self, restore_file=None, clear_existing=True, abort_on_err
             return self.restore(config, clear_existing=clear_existing,
                                 abort_on_error=abort_on_error)
 
+    def invalidate_caches(self):
+        '''
+        Invalidate any caches used throughout the hierarchy
+        '''
+        bs_cache.clear()
+
     targets = property(_list_targets,
             doc="Get the list of Target objects.")
     tpgs = property(_list_tpgs,