Add skip_bmc_config parameter to create_machine to skip re-config of BMC

[acormier1]

The create_machine API in Maas supports a skip_bmc_config flag. When set to true, this flag skips the bmc config so that a new user is not created. This is a workaround for some lenovo BMC's which have an issue during this provisioning step.

The result in maas when providing this parameter:

[SK1Y101]

The changes look alright, though the MAAS API docs do suggest this parameter is an integer rather than a boolean https://git.launchpad.net/maas/tree/src/maasserver/api/machines.py#n2039, so we may need to do some testing

This parameter is also passable to the commissioning stage of a Machine, extending to include that may be useful.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 69.43%. Comparing base (bfe63cc) to head (b29f064).

Files	Patch %	Lines
maas/client/viscera/machines.py	50.00%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #294      +/-   ##
==========================================
- Coverage   69.43%   69.43%   -0.01%     
==========================================
  Files          76       76              
  Lines        6024     6026       +2     
  Branches     1347     1348       +1     
==========================================
+ Hits         4183     4184       +1     
  Misses       1612     1612              
- Partials      229      230       +1     

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[SK1Y101]

Linter isn't happy, could you run tox -e format to fix that?