Tests in org.eclipse.ant.tests.ui which rely on ConsoleLineTracker
fail infrequently in I-builds. This is due to:

1. Relying on a boolean flag for more than two states.

The flag indicates whether the last console is closed or not.
An initialized console is marked as closed, which can confuse
tests waiting on the closed console state.

2. Synchronizing on a transient object.

When a console is initialized, the object used for synchronization
is replaced. Tests may wait until timeout, due to notifyAll()
calls on a different object.

This change introduces a state enum and a single lock object,
to avoid the race conditions.

See: https://github.com/eclipse-platform/eclipse.platform/issues/2621