netperf: introduce an agent to launch client sessions

Currently we use many threads/heavy control sessions to launch many
clients, Autotest takes too much host resouse.

This patch introduced an agent script, we execute it insider client
system to launch multiple sessions, and Autotest only need to use one
background thread to control clients.

We can consider to process the raw results in this agent script in
future, if it can help to simplify the case.

Signed-off-by: Amos Kong <akong@redhat.com>
utils_misc: Add a function to normalize the data size

Normalize a data size in one order of magnitude to another (MB to GB,
for example). In this function you can also change the factor as you
need, the default factor is 1024.

changes from v1:
  - rename the function and variables
  - update the method for getting a fraction.
  - Add unittests

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge branch 'next' of git://github.com/autotest/virt-test into next
virt.qemu.enospc:Fix the image_name change errors

Currently, the image_name has changed, the old fashion is like:
/tmp/kvm_autotest_root/images/f18-64, but the new is
images/f18-64.

In test, need to use data_dir to get the images dir.

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>