Set jaeger collector endpoint as an environment variable (#1399)

To follow 12-factor app rules, make jaeger collector endpoint
as an environment variable instead of CLI args. It's easier to
replace the value in different deployments. Also, we can utilize
valueFrom to get value from the configmap.

pkg/fetcher/config/config.go

@@ -96,7 +96,7 @@ func MakeFetcherConfig(sharedMountPath string) (*Config, error) {
 		sharedMountPath:         sharedMountPath,
 		sharedSecretPath:        "/secrets",
 		sharedCfgMapPath:        "/configs",
-		jaegerCollectorEndpoint: os.Getenv("OPENCENSUS_TRACE_JAEGER_COLLECTOR_ENDPOINT"),
+		jaegerCollectorEndpoint: os.Getenv("TRACE_JAEGER_COLLECTOR_ENDPOINT"),
 		serviceAccount:          types.FissionFetcherSA,
 	}, nil
 }