[6.12.z] update entity object with parametrized server_config rather default

[Satellite-QE]

Cherrypick of PR: #1106

Description of changes

Currently server_config was not getting set while reading the entity API call using target_sat

        dom = target_sat.api.Domain(server_config=sc, id=dom.id).read()
        dom.organization = [filter_taxonomies['org']]
        with pytest.raises(HTTPError):
            dom.update(['organization']) 

After this PR the dom object or any other api component object can access the API calls using the custom server_config set by parameter .

[Satellite-QE]

trigger: test-robottelo
pytest: -k test_negative_assign_taxonomies_by_org_admin tests/foreman/api/test_role.py

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

❗ No coverage uploaded for pull request base (6.12.z@3aa5591). Click here to learn what that means.

Files	Patch %	Lines
nailgun/entity_mixins.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             6.12.z    #1110   +/-   ##
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  Coverage          ?   93.19%           
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  Files             ?        6           
  Lines             ?     2925           
  Branches          ?        0           
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  Hits              ?     2726           
  Misses            ?      199           
  Partials          ?        0           

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[pondrejk]

ack pending test result