FEATURE: adding variable serial batches

This feature changes the scalar value of `serial:` to a list, which
allows users to specify a list of values, so batches can be ramped
up (commonly called "canary" setups):

- hosts: all
  serial: [1, 5, 10, "100%"]
  tasks:
  ...

lib/ansible/utils/helpers.py

@@ -0,0 +1,34 @@
+# (c) 2016, Ansible by Red Hat <support@ansible.com>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible.compat.six import string_types
+
+def pct_to_int(value, num_items, min_value=1):
+    '''
+    Converts a given value to a percentage if specified as "x%",
+    otherwise converts the given value to an integer. 
+    '''
+    if isinstance(value, string_types) and value.endswith('%'):
+        value_pct = int(value.replace("%",""))
+        return int((value_pct/100.0) * num_items) or min_value
+    else:
+        return int(value)
+