Create test_switchdpidassignment.py

Regression tests to verify switch datapath ID assignment.
Update test_switchdpidassignment.py
introducing OVSBridge
fallback to ovsb when no OF controller is unavailable
First crack at fixing multiple links

* Makes MultiGraph more like networkx.multigraph
* Adds converTo method
* Synchronizes node1 with xxx1 in link options
Allow natural sort to accept non-strings.
Allow Mininet() to accept multi-link topos w/correct params.
add example and test for multiple links
Minor fixes
Return (src, dst) in original order, and allow keys + data
merge HostWithPrivateDirs into Host
unmount private directories after use
ensure we retrieve a single PID when run on a cluster node
fix silent failures when rt cannot be assigned
Remove unused edgeinfo
Fix edges() and add convertTo() to Topo() (with keys option)
Ignore link info when sorting links.
Remove unnecessary 0
Merge pull request #429 from cdburkard/patches/cluster_m

ensure we retrieve a single PID when run on a cluster node
Merge pull request #424 from cdburkard/devel/mergePrivate

merge HostWithPrivateDirs into Node