MDL-44977 tool_profiling: set xhprof default settings

Set xhprof default settings, even if xhprof is not installed.
If xhprof is not installed, hide profiling admin settings,
else show them.
This is needed, because if xhprof is installed, then it will
fail all non-js behats which navigate to setting under
site administration, as profiling settings get displayed on
default admin page.