merge HostWithPrivateDirs into Node

ensure we retrieve a single PID when run on a cluster node

Background: the reference controller is reactive and installs exact
match rules. By attempting to start a telnet session we make sure that
the ARP caches and TCP flow rules are set up (in one direction at
least) before the test starts.

This is intended to help with #413

add cli usage information

support wireshark versions greater than 1.11 in test_walkthrough

Mininet crashes when running ping between two hosts with no interfaces

if a test fails or exits with an error, run cleanup as a precaution

Fixes #412

wait for sshd to start in baresshd example

use node.pexec() to update IP address of intf instead of node.cmd()

Unfortunately, this can slow things down a bit - perhaps
100-200 ms in the case of ovs-controller, but I am hoping that
it may help slightly with #399.

update interface IP address with pexec so that backgrounded process output from the cli cannot interfere

This should fix the problem where we see the first test
taking negative time, as well as possibly other issues
with performance tests which may be sensitive to changes
in wall clock time.

Fixes #398

wait for switches to connect during test_nets

Merge branch 'patches/linear_bw' of https://github.com/cdburkard/mininet into cdburkard-patches/linear_bw

Merge branch 'patches/fix_sshd' of https://github.com/cdburkard/mininet into cdburkard-patches/fix_sshd

check for vlan dependency

continue to test cfs if rt is not enabled in kernel

This should help with #393 although it doesn't solve
the root issue of the example failing silently when
vconfig is missing.