When Piwik config file becomes un-readable, make it clear that the file still exists but is not readable (#10331)

* * In messages, make it more clear whether config file exists and/or is (not) readable
* When the config file exists but is not readable, provide users the choice between making the file readable, or starting a fresh install
* As long as Piwik is not installed, piwik.php should not return 500 when config file is not readable
* Fixes #10283
* UI tests: updated message when config file is not found

Fixing ArchiveWebTest, now that test.php is used (which disables the logger), we must enable it in a test class override method, since this test checks the log output.

Fixing LogTest now that NullLogger is used for test environment setup.

Make sure translations are loaded in EnvironmentValidationTest.php.

Make sure the logger is enabled for ArchiveCronTest.

Rename Piwik_TestingEnvironment to TestingEnvironment and move the class to Piwik\Tests\Framework namespace. Remove manual require statements.

Add archive_web as entry point to test in EnvironmentValidationTest and verify that piwik host is correctly set and used in CronArchive (via console or web) w/o needing explicit Config setup in CronArchive class.

Added environment validation system test (mostly failing) that tests Piwik's behavior when INI files are gone or corrupt from each Piwik endpoint (tracker/reporting UI/console). Hacked test code to make it possible and for some tests to pass.