Support for iDrac9 on Dell PowerEdge R6415 and R6515

• Adds iDrac9 support for Dell PowerEdge R6415 and R6515

Fix a bug with managing the users on m1000e chassis

We were writing all the users to id=2 and the last write wins.

Generic logging Interface

• removes logrus logging in the package and allows clients to pass in a logger of their choice.
• example usage can be found in examples/main.go
• if no logger is provided, the default logger is a logrus implementation. code is at logging/logging.go

Add discover hint

• discover.ScanAndConnect() supports optional hinting, which probe to try first. The idea is that clients can use prior knowledge to speed up the connect and reduce the load on BMC's by reducing failing connection attempts.

Add support for Dell PowerEdge R630 (idrac8) / R640 (idrac9)

• PSM-2322 Fix a race condition in creating SSHClient
• PSM-2318 Add support for Dell PowerEdge R630 (idrac8) / R640 (idrac9)
• PSM-2320 Fix a race condition in tests