Refactor checkTouchApplicable()
We can remove direct overrides of checkTouchApplicable() by making
the method smarter in its checking of preconditions. Notably we
do not check TreeNode presence multiple times, but rather perform
a step-wise unpacking of state.
This has the benefit of having a clean place where we check if
automatic lifecycle is in effect and that happens only if the node
does not exist.
JIRA: YANGTOOLS-943
Change-Id: I72f4316c77d8f36efaf95209c36e898c9b4873cd
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>