CHANGE: http://review.gluster.com/2753 (cli: Enable output in XML) merged in master by Vijay Bellur (vijay)

Tested on v3.3.0qa44. Appending '--xml' to a gluster command produces xml output.
Eg:
-!- ~ » gluster volume info test --xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cliOutput><opRet>0</opRet><opErrno>0</opErrno><opErrstr></opErrstr><volInfo><volumes><volume><name>test</name><id>0fac9efa-3f73-4fea-9460-4df05f835e53</id><type>0</type><status>1</status><brickCount>1</brickCount><distCount>1</distCount><stripeCount>1</stripeCount><replicaCount>1</replicaCount><transport>0</transport><bricks><brick>arch:/export/test</brick></bricks><optCount>0</optCount><options/></volume><count>1</count></volumes></volInfo></cliOutput>

-!- ~ » gluster volume stop test --xml
Stopping volume will make its data inaccessible. Do you want to continue? (y/n) y
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cliOutput><volStop><flags>0</flags><volname>test</volname></volStop></cliOutput>

-!- ~ » gluster volume status test --xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cliOutput><opRet>-1</opRet><opErrno>0</opErrno><opErrstr>Volume test is not started</opErrstr><cliOp>volStatus</cliOp><output>Volume test is not started</output></cliOutput>

-!- ~ »