Initialize DependencyResolutionContext with default dependency mgmt

In the absence of a @GrabMetadata annotation,
DependencyResolutionContext provided no dependency management. This
was leading to incorrect dependency versions being pulled in. This
commit intializes the context with default dependency management that
will be replaced should @GrabMetadata be encountered.

Fixes #1021

spring-boot-cli/src/test/resources/repro-samples/data-jpa.groovy

@@ -0,0 +1,12 @@
+@Grab('spring-boot-starter-data-jpa')
+@Grab('h2')
+class Sample implements CommandLineRunner {
+
+	// No Data JPA-based logic. We just want to check that the dependencies are
+	// resolved correctly and that the app runs
+
+	@Override
+	void run(String... args) {
+		println "Hello World"
+	}
+}