RPM packages do not depend on procps

Synopsis
The RPM packaging declares no dependency on procps, although several
things shipped in MariaDB-server need it:

• mariadbd-safe runs ps(1): scripts/CMakeLists.txt substitutes
  @FIND_PROC@ into it, and every platform variant of that string is a
  "ps" invocation. mysqld_safe.sh also runs "ps xaww" to reap hung
  mariadbd processes before a restart
• wsrep_sst_common.sh, wsrep_sst_rsync.sh and wsrep_sst_mariabackup.sh
  poll "ps -p $pid" to see whether the SST parent is still alive
• mysql.server and mini-benchmark use pgrep(1)

rpm's automatic dependency generation does not cover commands invoked
from shell scripts, so nothing fills the gap. The Debian packaging has
declared procps for mariadb-server all along (debian/control).

procps is in the base install on RHEL, Fedora and SLES, so this is not
visible on a normal system. It shows up in minimal containers and
chroots, where "ps -p $pid" failing because ps is missing is
indistinguishable from "the process is gone".

Proposed change
add a Requires on /usr/bin/ps to the server package. A file
dependency avoids the procps-ng (Fedora/RHEL) vs procps (SLES) naming
difference; pgrep comes from the same package. The galera package
inherits it via its dependency on the server package, as on Debian.