tasks/selinux: fix escaping on ignore_known_denials

tasks/selinux: fix escaping on ignore_known_denials

a106217a swapped this line to use a raw string.  This left the initial
and final \' in the output resulting in a grep -av line which didn't
work as intended:

sudo grep -a 'avc: .*denied' /var/log/audit/audit.log | grep -av \'\(comm="dmidecode"\|chronyd.service\|name="cephtest"\|scontext=system_u:system_r:nrpe_t:s0\|scontext=system_u:system_r:pcp_pmlogger_t\|scontext=system_u:system_r:pcp_pmcd_t:s0\|comm="rhsmd"\|scontext=system_u:system_r:syslogd_t:s0\|tcontext=system_u:system_r:nrpe_t:s0\|comm="updatedb"\|comm="smartd"\|comm="rhsmcertd-worke"\|comm="setroubleshootd"\|comm="rpm"\|tcontext=system_u:object_r:container_runtime_exec_t:s0\|comm="ksmtuned"\|comm="sssd"\|comm="sss_cache"\|context=system_u:system_r:NetworkManager_dispatcher_t:s0\)\'

| grep -av \'

Instead, use r""" """ and don't escape the initial and trailing '.

Fixes: https://tracker.ceph.com/issues/58610
Introduced: a106217a990efa3b5af540d3cef712047f7b1d2a
Signed-off-by: Samuel Just <sjust@redhat.com>