Improve has_realtime_kernel method

[saikishor]

These changes allow the detection of realtime kernel even from the uname output. It should be more robust.

Fixes: #257

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 69.00%. Comparing base (db891ef) to head (57f4868).

Files with missing lines	Patch %	Lines
src/realtime_helpers.cpp	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #260      +/-   ##
==========================================
- Coverage   70.12%   69.00%   -1.13%     
==========================================
  Files           8        8              
  Lines         492      500       +8     
  Branches       84       86       +2     
==========================================
  Hits          345      345              
- Misses         92      100       +8     
  Partials       55       55              

Flag	Coverage Δ
unittests	69.00% <0.00%> (-1.13%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/realtime_helpers.cpp	36.79% <0.00%> (-3.01%)	⬇️