Fix resolution failure due to unprocessed bundle events.

A previous fix introduced asynchronous event processing in the bundle event hook during certain, short time intervals,
namely while the root subsystem is initializing. This fix prevents potential deadlocks. However, it also introduced an
issue where subsystem installations can fail due to resolution errors stemming from unprocessed bundle events when a
client performs an installation in response to a synchronous subsystem service event. A resolution failure occurs because
there is a bundle providing the required capability but subsystems is unaware it exists due to the unprocessed bundle
event.

This fix mitigates the issue by insuring all pending events have been processed before the root subsystem transitions to
the STARTING state. It is not currently possible, and perhaps unnecessary, to ensure pending events have been processed
before transitioning to the INSTALLED state without a major refactoring. To avoid these potential resolution failures,
clients should not attempt to install subsystems until the root subsystem has achieved at least the STARTING, and
ideally ACTIVE, states.

git-svn-id: https://svn.apache.org/repos/asf/aries/trunk@1442572 13f79535-47bb-0310-9956-ffa450edef68