CentOS-Stream-8/9 dependency fixes (#2893)

* CentOS-Stream-8/9 dependency fixes

Centos-Stream-8/9: change the 'ansible' dependency to 'ansible-core'.
Everybody else (at least for now) can get its hands on an 'ansible'
package (EPEL packages it for RHEL: it has a dependency on
'ansible-core' and includes some curated roles).

* Fixes from review comments on companion PR #2896

agent/rpm/pbench-agent.spec.j2

@@ -8,16 +8,22 @@ URL:            https://github.com/distributed-system-analysis/pbench
 Source0:        pbench-agent-%{version}.tar.gz
 Buildarch:      noarch
 
-%if 0%{?rhel} < 9
-Requires:  ansible
-%else
+# EPEL provides ansible (a curated set of roles with a dependency on ansible-core)
+# on RHEL 8 and RHEL9. Only CentOS-Stream seems to not have an ansible package
+# available.
+
+%if 0%{?centos} >= 8
 Requires:  ansible-core
+%else
+Requires:  ansible
 %endif
 
+
 %if 0%{?rhel} == 7
 Requires:  python3, python3-pip
 %endif
 
+# This condition will be true on a CentOS-Stream-8 system as well
 %if 0%{?rhel} == 8
 Requires:  python36, python3-pip
 # RPMs for modules in requirements.txt
@@ -26,6 +32,7 @@ Requires:  python3-cffi, python3-click, python3-requests
 Requires:  python3-docutils, python3-psutil
 %endif
 
+# This condition will be true on a CentOS-Stream-9 system as well
 %if 0%{?rhel} == 9
 Requires:  python3-pip
 # RPMs for modules in requirements.txt
@@ -34,6 +41,7 @@ Requires:  python3-cffi, python3-requests
 Requires:  python3-docutils, python3-psutil
 %endif
 
+
 %if 0%{?fedora} != 0
 Requires:  python3, python3-pip
 # RPMs for modules in requirements.txt