frontend.pkgdeps: Adding python-psutil to the list of required packages

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
utils.external_packages: Add python-psutil build info

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
frontend.afe.rpc_interface: Add get_server_status() method

In order to display a dashboard of the autotest server
status, we need to know some things:

 1) Free disk space in the autotest results directory
 2) Whether the autotest scheduler and the scheduler
    monitor are up

So use the very nice, 3rd party python module psutil:

https://code.google.com/p/psutil/

To inspect system information and return it through
the RPC call interface.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>