ss: Bug 486689: Add methods for getting an optional attribute quark

ss: Bug 486689: Add methods for getting an optional attribute quark

Change AttributeTree.getQuarkDontAdd() to return -1 instead of throwing
an AttributeNotFoundException.

Add methods optQuarkAbsolute() and optQuarkRelative() to the
ITmfStateSystem API.

Define and use quark constants ROOT_ATTRIBUTE and INVALID_ATTRIBUTE.

Use the new methods in the implementation of StateSystem.getQuarks().

Change-Id: I9f28e8aa8f3ba7377bebf8a5e8042ae7675aecab
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/65328
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>