[xenial, 1.10] Removing host maps fails

[Mike Pontillo]

Upon deleting a node, I saw the following exception on the cluster:

http://paste.ubuntu.com/13947680/

2015-12-11 16:08:50-0800 [-] Unhandled failure dispatching AMP command. This is probably a bug. Please ensure that this error is handled within application code or declared in the signature of the b'RemoveHostMaps' command. [maastest:pid=10973:cmd=RemoveHostMaps:ask=f]
 Traceback (most recent call last):
   File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 1203, in mainLoop
     self.runUntilCurrent()
   File "/usr/lib/python3/dist-packages/twisted/internet/base.py", line 798, in runUntilCurrent
     f(*a, **kw)
   File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 434, in errback
     self._startRunCallbacks(fail)
   File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 501, in _startRunCallbacks
     self._runCallbacks()
 --- <exception caught here> ---
   File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 588, in _runCallbacks
     current.result = callback(current.result, *args, **kw)
   File "/usr/lib/python3/dist-packages/provisioningserver/twisted/protocols/amp.py", line 1131, in checkKnownErrors
     key = error.trap(*command.allErrors)
   File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 342, in trap
     self.raiseException()
   File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 368, in raiseException
     raise self.value.with_traceback(self.tb)
   File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 241, in inContext
     result = inContext.theWork()
   File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 257, in <lambda>
     inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
   File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
     return self.currentContext().callWithContext(ctx, func, *args, **kw)
   File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
     return func(*args,**kw)
   File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 197, in wrapper
     return func(*args, **kwargs)
   File "/usr/lib/python3/dist-packages/provisioningserver/rpc/dhcp.py", line 244, in remove_host_maps
     omshell.remove(identifier)
   File "/usr/lib/python3/dist-packages/provisioningserver/dhcp/omshell.py", line 219, in remove
     returncode, output = self._run(stdin)
   File "/usr/lib/python3/dist-packages/provisioningserver/dhcp/omshell.py", line 125, in _run
     stdout, stderr = proc.communicate(stdin)
   File "/usr/lib/python3.5/subprocess.py", line 1068, in communicate
     stdout, stderr = self._communicate(input, endtime, timeout)
   File "/usr/lib/python3.5/subprocess.py", line 1687, in _communicate
     input_view = memoryview(self._input)
 builtins.TypeError: memoryview: a bytes-like object is required, not 'str'

This also resulted in the following error in the UI:

The delete action for 1 node failed with error: (b'UNHANDLED', 'Unknown Error [maastest:pid=10973:cmd=RemoveHostMaps:ask=f]')

[Blake Rouse (blake-rouse)]

This is also an issue with commissioning. I am fixing this as part of fixing commissioning.