Dev: utils: Change get_dc function as the behavior of crmadmin -D changed

[liangxin1300]

The behavior of crmadmin -D changed when no DC elected
original:

# crmadmin -D -t 1
error: Timed out after 1000ms waiting for reply from controller API on DC
error: Command failed: Resource temporarily unavailable

now:

# crmadmin -D -t 1
Designated Controller is: not yet elected

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.56%. Comparing base (2731077) to head (231425e).
Report is 2 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
integration	53.85% <100.00%> (+0.02%)	⬆️
unit	52.76% <0.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
crmsh/utils.py	66.45% <100.00%> (+0.01%)	⬆️

... and 4 files with indirect coverage changes

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