Classify warnings correctly in logging output

[echeran]

We have a lot of errors in the end-to-end script that we're continuing on with. For each instance, we should do one of the following:

1. If it is okay and normal to proceed, then reclassify it is a warning
2. If it not okay, and we should really fix that ASAP, then it is an error. It is optional whether to stop the program *
3. If it is really bad, and we should stop the program as a result of the problem, then it should be classified as "fatal" if that log level exists, and the program should terminate immediately

* I still prefer stopping the program when an error occurs so that we fail loudly and early, which is the opposite of failing silently. By "program", I mean the problems when running testing framework, not anything related to the test results.

Examples from recent output:

• https://github.com/unicode-org/conformance/pull/237/checks#step:7:17

  Error: 6-13 20:11:29,228] [ERROR]  Generating datetime data not configured for icu version icu69
  Error: 6-13 20:11:29,229] [ERROR]  Generating list_fmt data not configured for icu version icu69
  Warning: 13 20:11:29,230] [WARNING]  ** READ: Error = [Errno 2] No such file or directory: 'icu69/languageNameTable.txt'
  Warning: 13 20:11:29,230] [WARNING]  ** READ: Error = [Errno 2] No such file or directory: 'icu69/likelySubtags.txt'
  [2024-06-13 20:11:29,294] [INFO]    generateNumberFmtTestDataObjects gives 5850 tests
  Error: 6-13 20:11:29,308] [ERROR]  Generating datetime data not configured for icu version icu70
  Error: 6-13 20:11:29,309] [ERROR]  Generating list_fmt data not configured for icu version icu70
  Warning: 13 20:11:29,310] [WARNING]  ** READ: Error = [Errno 2] No such file or directory: 'icu70/languageNameTable.txt'
  Warning: 13 20:11:29,311] [WARNING]  ** READ: Error = [Errno 2] No such file or directory: 'icu70/likelySubtags.txt'
  

• https://github.com/unicode-org/conformance/pull/237/checks#step:7:7811

  Error: 6-13 20:19:38,827] [ERROR]  !!! 'list_fmt_test' for file ../TEMP_DATA/testOutput/node/icu73/list_fmt_test.json
  Error: 6-13 20:19:38,828] [ERROR]  !!! 'rdt_fmt_test' for file ../TEMP_DATA/testOutput/node/icu73/rdt_fmt_test.json
  Error: 6-13 20:19:38,828] [ERROR]  !!! 'datetime_fmt_test' for file ../TEMP_DATA/testOutput/node/icu73/datetime_fmt_test.json
  Error: 6-13 20:19:38,828] [ERROR]  !!! 'plural_rules_test' for file ../TEMP_DATA/testOutput/node/icu73/plural_rules_test.json
  Error: 6-13 20:19:38,828] [ERROR]  !!! 'rdt_fmt_test' for file ../TEMP_DATA/testOutput/node/icu72/rdt_fmt_test.json
  Error: 6-13 20:19:38,828] [ERROR]  !!! 'datetime_fmt_test' for file ../TEMP_DATA/testOutput/node/icu72/datetime_fmt_test.json
  Error: 6-13 20:19:38,828] [ERROR]  !!! 'plural_rules_test' for file ../TEMP_DATA/testOutput/node/icu72/plural_rules_test.json