Don't start unnecessary operations that only concern the "Tracing" tab
upon initialization of the PDE-Run configuration (in the dialog "Run
configurations..."). Instead, only do them when the tab is first
selected. This speeds up opening the dialog "Run configurations..." (and
also switching to a PDE-Run configuration when the dialog is already
opened).

Show a progress indicator when doing some (possibly) long-running
operations in the "Tracing" tab.

Fixes to https://github.com/eclipse-pde/eclipse.pde/issues/679