tests: never use -o pipefail

tests: never use -o pipefail

It was hard to find out that pipefail was the reason why our
test-suite could have random failures for aribtrary tests,
for example the ones which are using ts_device_has_uuid() or
ts_mount().

Bash's pipefall option is evil! It may return error for such a
simple line like this one
$ echo -e "xxx\nyyy" | grep -q "xxx"
because the left echo command will get SIGPIPE when grep exits after
the first match. So the command line above could return an error
eventhough it does exactly what we want.

This patch removes any pipefail from our tests. The funny thing is
that I couldn't find any case where we relied on this feature anyway.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>