util: Use consistent error preservation and restoration calls

Provide some consistency over error message variable name and usage
when saving error messages across possible other errors or possibility
of resetting of the last error.

Instead of virSaveLastError paired up with virSetError and virFreeError,
we should use the newer virErrorPreserveLast and virRestoreError.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

src/util/vircgroup.c

@@ -1168,13 +1168,12 @@ virCgroupNewMachineSystemd(const char *name,
     }
 
     if (virCgroupAddProcess(*group, pidleader) < 0) {
-        virErrorPtr saved = virSaveLastError();
+        virErrorPtr saved;
+
+        virErrorPreserveLast(&saved);
         virCgroupRemove(*group);
         virCgroupFree(group);
-        if (saved) {
-            virSetError(saved);
-            virFreeError(saved);
-        }
+        virErrorRestore(&saved);
     }
 
     return 0;
@@ -1220,13 +1219,12 @@ virCgroupNewMachineManual(const char *name,
         goto cleanup;
 
     if (virCgroupAddProcess(*group, pidleader) < 0) {
-        virErrorPtr saved = virSaveLastError();
+        virErrorPtr saved;
+
+        virErrorPreserveLast(&saved);
         virCgroupRemove(*group);
         virCgroupFree(group);
-        if (saved) {
-            virSetError(saved);
-            virFreeError(saved);
-        }
+        virErrorRestore(&saved);
     }
 
  done:

src/util/virfirewall.c

@@ -838,7 +838,9 @@ virFirewallApply(virFirewallPtr firewall)
         if (virFirewallApplyGroup(firewall, i) < 0) {
             VIR_DEBUG("Rolling back groups up to %zu for %p", i, firewall);
             size_t first = i;
-            g_autoptr(virError) saved_error = virSaveLastError();
+            virErrorPtr saved_error;
+
+            virErrorPreserveLast(&saved_error);
 
             /*
              * Look at any inheritance markers to figure out
@@ -858,7 +860,7 @@ virFirewallApply(virFirewallPtr firewall)
                 virFirewallRollbackGroup(firewall, j);
             }
 
-            virSetError(saved_error);
+            virErrorRestore(&saved_error);
             VIR_DEBUG("Done rolling back groups for %p", firewall);
             goto cleanup;
         }