test: cephtool/test.sh: fix expect_false with pipe

test: cephtool/test.sh: fix expect_false with pipe

this fixes failures like,

/home/jenkins-build/build/workspace/ceph-pull-requests/qa/workunits/cephtool/test.sh:
line 32: ceph osd blacklist ls | grep 192.168.0.1: command not found

where the failure is not the "failure" we are expecting.

in our tests, following command

expect_false "ceph osd blacklist ls | grep 192.168.0.1"

is designed to to verify that "ceph osd blacklist ls | grep 192.168.0.1"
fails with non-zero return code. but expect_false() evaluates the command
line using plain "$@", which will send the arguments direct to the shell,
and $0 is "ceph auth get client.xx | grep caps | grep mon", which does
not exist and is not built-in command. so we need to check the grep
command instead.

for multiple piped command line, use

expect_false sh <<< "echo foo  | grep bar | grep baz"

Signed-off-by: Kefu Chai <kchai@redhat.com>