Lazily init Jaeger

Jaeger will always be initilized due to MP context
propagation. This change delays init till it is actually used.

extensions/jaeger/runtime/src/main/java/io/quarkus/jaeger/runtime/QuarkusJaegerTracer.java

@@ -3,6 +3,7 @@
 import io.jaegertracing.Configuration;
 import io.jaegertracing.internal.JaegerTracer;
 import io.jaegertracing.spi.MetricsFactory;
+import io.opentracing.Scope;
 import io.opentracing.ScopeManager;
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
@@ -17,6 +18,35 @@ public class QuarkusJaegerTracer implements Tracer {
     private boolean logTraceContext;
     private MetricsFactory metricsFactory;
 
+    private final ScopeManager scopeManager = new ScopeManager() {
+
+        volatile ScopeManager delegate;
+
+        @Override
+        public Scope activate(Span span, boolean b) {
+            return sm().activate(span, b);
+        }
+
+        @Override
+        public Scope active() {
+            if (delegate == null) {
+                return null;
+            }
+            return sm().active();
+        }
+
+        ScopeManager sm() {
+            if (delegate == null) {
+                synchronized (this) {
+                    if (delegate == null) {
+                        delegate = getScopeManager();
+                    }
+                }
+            }
+            return delegate;
+        }
+    };
+
     void setLogTraceContext(boolean logTraceContext) {
         this.logTraceContext = logTraceContext;
     }
@@ -44,7 +74,7 @@ private Tracer tracer() {
                     tracer = Configuration.fromEnv()
                             .withMetricsFactory(metricsFactory)
                             .getTracerBuilder()
-                            .withScopeManager(getScopeManager())
+                            .withScopeManager(scopeManager)
                             .build();
                 }
             }
@@ -77,7 +107,7 @@ public <C> SpanContext extract(Format<C> format, C carrier) {
 
     @Override
     public ScopeManager scopeManager() {
-        return tracer().scopeManager();
+        return scopeManager;
     }
 
     @Override