Returns a string summarizing any errors that occurred during the build
Convenience method for summarizing errors (or exceptions) that occurred during a build into a single line of text.
If no error was logged this returns an empty string. If a single error was logged this reports the error messages. Otherwise it reports the number of errors, for example "5 errors".
Note: To examine all errors, warnings and other messages recorded during a build you can enumerating through the build steps and check BuildStep.messages.
And to retrieve the count of errors call BuildSummary.totalErrors.