Fix anyData content normalization incl no data case

Fix anyData content normalization incl no data case

Parsing of anydata content is now performed with inference
pointing to anydata node itself as a root (parentNode),
not first child. This allows proper normalization of any
anydata content incl empty case.

List/leaf-list element parsing logic was updated to detach
schema node value check as a condition bc top level node
identifiers are not matching when anydata content is parsed.
Local name and namespace match is used instead.

JIRA: YANGTOOLS-1011
Change-Id: I09ae84c44ada198b888d901dff0425b29400fb4f
Signed-off-by: Anna Bencurova <Anna.Bencurova@pantheon.tech>
Signed-off-by: Ruslan Kashapov <ruslan.kashapov@pantheon.tech>