ipa-client-automount: handle NFS configuration file changes

nfs-utils in Fedora 30 and later switched its configuration
file from /etc/sysconfig/nfs to /etc/nfs.conf, providing a
conversion service (nfs-convert.service) for upgrades.
However, for new installs the original configuration file
is missing. This change:
* adds a tuple-based osinfo.version_number method to handle
  more kinds of OS versioning schemes
* detects RHEL and Fedora versions with the the new nfs-utils
  behavior
* avoids backing up the new NFS configuration file as we do
  not have to modify it.

See: https://bugzilla.redhat.com/show_bug.cgi?id=1676981

Fixes: https://pagure.io/freeipa/issue/7868
Signed-off-by: François Cami <fcami@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

client/ipa-client-automount.in

@@ -335,14 +335,16 @@ def configure_nfs(fstore, statestore):
     """
     Configure secure NFS
     """
-    replacevars = {
-        constants.SECURE_NFS_VAR: 'yes',
-    }
-    ipautil.backup_config_and_replace_variables(fstore,
-        paths.SYSCONFIG_NFS, replacevars=replacevars)
-    tasks.restore_context(paths.SYSCONFIG_NFS)
-
-    print("Configured %s" % paths.SYSCONFIG_NFS)
+    # Newer Fedora releases ship /etc/nfs.conf instead of /etc/sysconfig/nfs
+    # and do not require changes there. On these, SECURE_NFS_VAR == None
+    if constants.SECURE_NFS_VAR:
+        replacevars = {
+            constants.SECURE_NFS_VAR: 'yes',
+        }
+        ipautil.backup_config_and_replace_variables(fstore,
+            paths.SYSCONFIG_NFS, replacevars=replacevars)
+        tasks.restore_context(paths.SYSCONFIG_NFS)
+        print("Configured %s" % paths.SYSCONFIG_NFS)
 
     # Prepare the changes
     # We need to use IPAChangeConf as simple regexp substitution