Case-insensitive matching of errors/warnings in admin diagnostics

To test the change (assuming a stopped server):
- invalidate Ice grid configuration : `echo "RaiseAnIceXMLParserExceptionAtStartup" >> $OMERO_HOME/etc/grid/templates.xml`
- run `omero admin start` : server starts up despite invalid XML syntax
- run `omero admin diagnostics` : log files report for `master.err` should now display positive errors and warnings counts