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:

[skyecas]

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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[skyecas]

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