libcgroup: Add test cases for new get_task API

libcgroup: Add test cases for new get_task API

This is the test case for the new API. This test takes one argument, the
group name.

Sample run on my system with this test case returns,

[dhaval@gondor tests]$ ../libtool --mode=execute ./walk_task a
Printing the details of groups a
Pid is 6092
Pid is 11315
Pid is 11318
Pid is 11319
Pid is 11324
Pid is 13234
[dhaval@gondor tests]$

Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: Bharata B Rao <bharata@linux.vnet.ibm.com>