increase verbosity level of various messages

[kroening]

CBMC generates too much console output. This commit increases the verbosity level required for various progress and performance statistics messages.

• 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).
• n/a 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

All modified and coverable lines are covered by tests ✅

Project coverage is 78.37%. Comparing base (8646bfa) to head (da777a0).
Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8330      +/-   ##
===========================================
- Coverage    78.37%   78.37%   -0.01%     
===========================================
  Files         1726     1726              
  Lines       188322   188325       +3     
  Branches     18460    18445      -15     
===========================================
+ Hits        147606   147607       +1     
- Misses       40716    40718       +2     

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[peterschrammel]

lgtm