ci: switch back to ssh connections in system tests

We have switched to podman connection to run the tests faster.
However, even though podman is approximately twice as fast in
local run with recent podman version, it is quite slower in
PR CI.

Further, the podman and related components available in
Github Ubuntu runners are quite outdated and they still have some
issues. We were often hitting a bug where `podman exec` would yield
incomplete stdout.

See: containers/podman#9096

src/tests/system/mhc.yaml

@@ -9,21 +9,13 @@ domains:
   hosts:
   - hostname: client.test
     role: client
-    conn:
-      type: podman
-      container: client
-      sudo: True
     artifacts:
     - /etc/sssd/*
     - /var/log/sssd/*
     - /var/lib/sss/db/*
 
   - hostname: master.ldap.test
     role: ldap
-    conn:
-      type: podman
-      container: ldap
-      sudo: True
     config:
       binddn: cn=Directory Manager
       bindpw: Secret123
@@ -34,10 +26,6 @@ domains:
 
   - hostname: master.ipa.test
     role: ipa
-    conn:
-      type: podman
-      container: ipa
-      sudo: True
     config:
       client:
         ipa_domain: ipa.test
@@ -59,10 +47,6 @@ domains:
 
   - hostname: dc.samba.test
     role: samba
-    conn:
-      type: podman
-      container: samba
-      sudo: True
     config:
       binddn: CN=Administrator,CN=Users,DC=samba,DC=test
       bindpw: Secret123
@@ -73,19 +57,11 @@ domains:
 
   - hostname: nfs.test
     role: nfs
-    conn:
-      type: podman
-      container: nfs
-      sudo: True
     config:
       exports_dir: /dev/shm/exports
 
   - hostname: kdc.test
     role: kdc
-    conn:
-      type: podman
-      container: kdc
-      sudo: True
     config:
       realm: TEST
       domain: test