Gcov: remove SWTBot from tests.

Convert all GCov UI tests to use Eclipse API instead of SWTBot.
This required some features to be modified so they could be
testable without relying on UI interaction.

Change-Id: I2a20e4edf828a7561d81261829d93c9da6309c7d
Signed-off-by: Andrew Ferrazzutti <aferrazz@redhat.com>
Reviewed-on: https://git.eclipse.org/r/36181
Tested-by: Hudson CI
Reviewed-by: Alexander Kurtakov <akurtako@redhat.com>
Tested-by: Alexander Kurtakov <akurtako@redhat.com>