Do not use the absolute path in redis' pidof calls

The reason for this is that newer kernels (we saw this on a 4.18 kernel)
can limit access to /proc/<pid>/{cwd,exe,root} and so pidof will fail to
identify the process when using the full path names.
This access limitation happens even with the root user:
()[root@ra1 /]$ ls -l /proc/32/ |grep redis-server
ls: cannot read symbolic link '/proc/32/cwd': Permission denied
ls: cannot read symbolic link '/proc/32/root': Permission denied
ls: cannot read symbolic link '/proc/32/exe': Permission denied

For this reason the 'pidof /usr/bin/redis-server' calls will fail
when running inside containers that have this kernel protection
mechanism.

We tested this change and successfuly obtained a running redis cluster:
podman container set: redis-bundle [192.168.222.1:5000/redis:latest]

Replica[0]
   redis-bundle-podman-0     (ocf::heartbeat:podman):        Started ra1
   redis-bundle-0    (ocf::pacemaker:remote):        Started ra1
   redis     (ocf::heartbeat:redis): Master redis-bundle-0
Replica[1]
   redis-bundle-podman-1     (ocf::heartbeat:podman):        Started ra2
   redis-bundle-1    (ocf::pacemaker:remote):        Started ra2
   redis     (ocf::heartbeat:redis): Slave redis-bundle-1
Replica[2]
   redis-bundle-podman-2     (ocf::heartbeat:podman):        Started ra3
   redis-bundle-2    (ocf::pacemaker:remote):        Started ra3
   redis     (ocf::heartbeat:redis): Slave redis-bundle-2

Signed-off-By: Damien Ciabrini <dciabrin@redhat.com>
Signed-off-by: Michele Baldessari <michele@acksyn.org>