[feat] Print the first lines of stderr and stdout in case of sanity failures

[ekouts]

We do something similar in case of BuildError, where we add the stderr in the message of the exception: https://github.com/reframe-hpc/reframe/blob/develop/reframe/core/exceptions.py#L164
I print stderr and stdout in statistics because we have checks at CSCS that raise their own SanityError (like this example) and I thought other people may be using it like this.
What do you think? Should I change the PR and go with the approach of BuildError?

Closes #2668 .

[codecov-commenter]

Codecov Report

Base: 86.61% // Head: 86.61% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (1ea48de) compared to base (12827d9).
Patch coverage: 85.71% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2762      +/-   ##
===========================================
- Coverage    86.61%   86.61%   -0.01%     
===========================================
  Files           60       60              
  Lines        11215    11235      +20     
===========================================
+ Hits          9714     9731      +17     
- Misses        1501     1504       +3     

Impacted Files	Coverage Δ
reframe/frontend/statistics.py	95.18% <85.71%> (-0.89%)	⬇️

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[vkarak]

I agree that it's better to add in the failure report instead of bloating the SanityError.

[vkarak]

lgtm