reduce default verbosity of cprover binary

[kroening]

This sets a new default for the verbosity of the cprover binary, to match the level of the cbmc binary.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.36%. Comparing base (2ffc4c9) to head (cfbbeb4).
Report is 6 commits behind head on develop.

Files	Patch %	Lines
src/cprover/cprover_parse_options.cpp	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8352      +/-   ##
===========================================
+ Coverage    78.09%   78.36%   +0.27%     
===========================================
  Files         1726     1726              
  Lines       189039   188384     -655     
  Branches     18399    18446      +47     
===========================================
+ Hits        147629   147631       +2     
+ Misses       41410    40753     -657     

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