Need clear error message in the UI during support zip generation

Issue

• During support zip generation, UI reported an error "Your support zip is ready to download, but some errors occurred". The support zip was successfully generated, but no details of any error shown in the application log.
  

Expected Result

• Jira should print more details about the error in the UI.

Actual behavior

• After turning on the debug logging for package 'com.atlassian.troubleshooting', the log indicated the support zip was successfully generated and the error happened because the 'limit file sizes' box was checked in the customize zip page.

   
  2019-05-30 09:05:08,161 support-zip WARN darrenv_admin 544x35189x1 nih67l 10.113.152.34,10.113.243.239 /rest/troubleshooting/latest/support-zip/local [c.a.t.stp.zip.ZipFileAppender] The file atlassian-jira-gc-2019-05-22_1808.log.0 was truncated to 25Mb in size.  If you need to include the whole file, untick the 'Limit File Sizes' option.
  2019-05-30 09:05:11,353 support-zip INFO darrenv_admin 544x35189x1 nih67l 10.113.152.34,10.113.243.239 /rest/troubleshooting/latest/support-zip/local [atlassian.plugin] Saved Support Zip to: /var/atlassian/application-data/jira/export/JIRA_support_2019-05-30-09-04-59.zip
  

Workaround

• Once uncheck the box 'limit file sizes' during support zip generation, no error was reported.