MULE-7399: Flows can start processing messages before referenced flows are completely started

Broken test: cannot use mule client to exercise an inbound endpoint if mule context is not fully started.

Fix: use HttpClient to exercise an HTTP endpoint.

(cherry picked from commit 19f7add7e2a9758d40c3dceee125220ab461cd71)

Conflicts:
	tests/integration/src/test/resources/composite-source-start-delay-config.xml