tests: grep portability fixes

tests: grep portability fixes

We try to avoid using the "-q" or "-e" options, as they are
largely useless, as explained in aadbe44f.

There is one exception for "-e" here, which is in t7701 used
to produce an "or" of patterns. This can be rewritten as an
egrep pattern.

This patch also removes use of "grep -F" in favor of the
more widely available "fgrep".

[sp: Tested on AIX 5.3 by Mike Ralphson,
     Tested on MinGW by Johannes Sixt]

Signed-off-by: Jeff King <peff@peff.net>
Tested-by: Mike Ralphson <mike@abacus.co.uk>
Tested-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>