Pass down autoconf's EGREP to the tests.

Pass down autoconf's EGREP to the tests.

Care was taken to make sure where to quote and where not to; variable
assignments with EGREP=@EGREP@ need quoting in order not to split the
variable into tokens; expansions in places where we used to invoke egrep
need not because they actually need to split $EGREP contents in case
it's "grep -E".

This fixes "egrep is obsolescent" warnings on newer coreutils.

Signed-off-by: Matthias Andree <matthias.andree@gmx.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>