BUG-1953: fix bad values in netconf monitoring test

Uses string values which do not match the format prescribed by the
model. Fix them.

Change-Id: I55efcdd87aea24bcfd805a865319fe324e663768
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "BUG-1953: fix bad values in netconf monitoring test"