Updating docs for max_fail_percentage plus CHANGELOG updates

CHANGELOG.md

@@ -16,7 +16,8 @@ Highlighted new features:
 * if --forks exceeds the numbers of hosts, it will be automatically reduced. Set forks to 0 and you get "as many forks as I have hosts" out of the box.
 * enabled error_on_undefined_vars by default, which will make errors in playbooks more obvious
 * role dependencies -- one role can now pull in another, with parameters of its own.
-* added the ability to have tasks execute even during a check run (always_run)
+* added the ability to have tasks execute even during a check run (always_run).
+* added the ability to set the maximum failure percentage for a group of hosts.
 
 New modules:
 
@@ -26,6 +27,9 @@ New modules:
 * cloud: linode -- modules for Linode provisioning that also includes inventory support
 * cloud: route53 -- manage Amazon DNS entries 
 * cloud: ec2_ami -- manages (and creates!) ec2 AMIs
+* database: mysql_replication -- manages mysql replication settings for masters/slaves
+* database: mysql_variables -- manages mysql runtime variables
+* database: redis -- manages redis databases (slave mode and flushing data)
 * net_infrastructure: arista_interface
 * net_infrastructure: arista_lag
 * net_infrastructure: arista_l2interface
@@ -37,7 +41,6 @@ New modules:
 * monitoring: boundary_meter -- adds or removes boundary.com meters
 * net_infrastructure: dnsmadeeasy - manipulate DNS Made Easy records
 * files: xattr -- manages extended attributes on files
-* database: redis -- manages redis databases (slave mode and flushing data)
 
 Misc changes:
 

docsite/latest/rst/playbooks2.rst

@@ -884,6 +884,27 @@ use case, you can define how many hosts Ansible should manage at a single time b
 In the above example, if we had 100 hosts, 3 hosts in the group 'webservers'
 would complete the play completely before moving on to the next 3 hosts.
 
+Maximum Failure Percentage
+``````````````````````````
+
+.. versionadded:: 1.3
+
+By default, Ansible will continue executing actions as long as there are hosts in the group that have not yet failed.
+In some situations, such as with the rolling updates described above, it may be desireable to abort the play when a 
+certain threshold of failures have been reached. To acheive this, as of version 1.3 you can set a maximum failure 
+percentage on a play as follows::
+
+    - hosts: webservers
+      max_fail_percentage: 30
+      serial: 10
+
+In the above example, if more than 3 of the 10 servers in the group were to fail, the rest of the play would be aborted.
+
+.. note::
+
+     The percentage set must be exceeded, not equaled. For example, if serial were set to 4 and you wanted the task to abort 
+     when 2 of the systems failed, the percentage should be set at 49 rather than 50.
+
 Delegation
 ``````````