Replace egrep/fgrep with grep -E/-F

There are days when I really, really, really hate GNU. Remember
when someone decided that 'head -1' would no longer work, and
that it was OK to break an infinite number of legacy production
scripts? Someone now decided that egrep/fgrep are deprecated,
and our CI logs (especially pr-should-include-tests) are now
filled with hundreds of warning lines, making it difficult
to find actual errors.

I expect that those warnings will be removed quickly after
furious community backlash, just like the 'head -1' fiasco
was quietly reverted, but ITM the warnings are annoying
so I capitulate.

Signed-off-by: Ed Santiago <[email protected]>