Add test & constant for set_versions flag

Also added set_versions help entry to cgr-engine doc.

cmd/cgr-engine/cgr-engine.go

@@ -66,7 +66,7 @@ var (
 	nodeID            = cgrEngineFlags.String(utils.NodeIDCfg, utils.EmptyString, "Node ID of the engine")
 	logLevel          = cgrEngineFlags.Int(utils.LogLevelCfg, -1, "Log level (0=emergency to 7=debug)")
 	preload           = cgrEngineFlags.String(utils.PreloadCgr, utils.EmptyString, "Loader IDs used to load data before engine starts")
-	setVersions       = cgrEngineFlags.Bool("set_versions", false, "Overwrite database versions (equivalent to cgr-migrator -exec=*set_versions)")
+	setVersions       = cgrEngineFlags.Bool(utils.SetVersionsCgr, false, "Overwrite database versions (equivalent to cgr-migrator -exec=*set_versions)")
 
 	cfg *config.CGRConfig
 )

cmd/cgr-engine/cgr-engine_flags_test.go

@@ -140,6 +140,13 @@ func TestCgrEngineFlags(t *testing.T) {
 			defaultVal: "",
 			want:       "TestPreloadID",
 		},
+		{
+			name:       "setVersions",
+			flags:      []string{"-set_versions"},
+			flagVar:    setVersions,
+			defaultVal: false,
+			want:       true,
+		},
 	}
 
 	for _, tt := range tests {