grep with --extended-regexp much slower on Ubuntu 16.04

[Ralf Mardorf]

On my Arch Linux install it doesn't make a difference if running
your grep line with LC_ALL=en_US.utf8 or LC_ALL=C on dash or bash,
with equal as well as different generated random.txt files, the result
is always

real	0m0.4[...]s
user	0m0.3[...]s
sys	0m0.0[...]s

so as already pointed out by other, running on the same hardware, there
still might be a difference regarding the load. Perhaps "top" shows a
fishy process taking too much CPU and/or RAM.