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.

add 1ms delay to all links to exaggerate TCP bandwidth decrease across an increasing number of links

Conflicts:
	examples/cpu.py

workaround: attach to cgroup first, then mount namespace

add Ryu controller support to Mininet

Skip test_cpu.py if RT_GROUP_SCHED is not enabled

use udp with iperf to measure loss. pings are not reliable

measure loss with udp iperf