Adds the tenant_filter_file to the config file

tenant_filter_file is the path to a file that contains a list of tenant
ids to migrate. If missing, swsync will migrate all the tenants.

etc/config.ini-sample

@@ -21,3 +21,9 @@ filler_keystone_client_concurrency = 5
 filler_swift_client_concurrency = 10
 # This is usually bound to the max open files.
 sync_swift_client_concurrency = 10
+
+[sync]
+# This fields holds the path the a file containing the list of tenant ids to
+# migrate. If this field is left blank or commented out, swsync will migrate all
+# the tenants.
+tenant_filter_file =

swsync/accounts.py

@@ -24,7 +24,7 @@ import keystoneclient.v2_0.client
 import swiftclient
 
 import swsync.containers
-from utils import get_config
+from utils import get_config, ConfigurationError
 
 
 class Accounts(object):
@@ -52,6 +52,22 @@ class Accounts(object):
                                                  password=password,
                                                  tenant_name=tenant_name)
 
+    def get_target_tenant_filter(self):
+        """Returns a set of target tenants from the tenant_list_file.
+        tenant_list_file is defined in the config file or given as a command
+        line argument.
+
+        If the file is not defined, returns None.
+        """
+        try:
+            tenant_filter_filename = get_config('sync', 'tenant_filter_file')
+
+            with open(tenant_filter_filename) as tenantsfile:
+                return {name.strip() for name in tenantsfile.readlines()}
+        except (ConfigurationError, IOError):
+            return None
+
+
     def account_headers_clean(self, account_headers, to_null=False):
         ret = {}
         for key, value in account_headers.iteritems():
@@ -160,7 +176,16 @@ class Accounts(object):
 
         self.keystone_cnx = self.get_ks_auth_orig()
 
-        for tenant in self.keystone_cnx.tenants.list():
+        # if user has defined target tenants, limit the migration
+        # to them
+        _targets_filters = self.get_target_tenant_filter()
+        if _targets_filters is not None:
+            _targets = (tenant for tenant in self.keystone_cnx.tenants.list()
+                        if tenant.id in _targets)
+        else:
+            _targets = self.keystone_cnx.tenants.list()
+
+        for tenant in _targets:
             user_orig_st_url = bare_oa_st_url + tenant.id
             user_dst_st_url = bare_dst_st_url + tenant.id