Fix guid tests overwriting home config

[jenshnielsen]

The context manager used to protect the config in the guid tests that overwrites home config was insuffisient as it did not relocate the home config. Use the default_config config manager instead that does this correctly.

In the process of debugging this issue I found that test_generic_formatter cannot be run standalone so fix that too.

Since we use the default_config context manager in multiple locations I also moved that to a common location

[codecov]

Codecov Report

Merging #2073 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2073   +/-   ##
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  Coverage   71.13%   71.13%           
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  Files         150      150           
  Lines       20050    20050           
=======================================
  Hits        14263    14263           
  Misses       5787     5787