Corrects broken format strings in check_i18n.py

In tools/check_i18n.py, the error messages printed out
had format strings that included 5 interpolations, but only
four variables were supplied. This patch simply corrects that
mismatch by including the name of the predicate or checker
that failed.

Closes-Bug: #1263813
Change-Id: I5cacee9ea000f56a9ef45f07367e85f20fa333c7
Use base.BaseTestCase in NVP config test

BaseTestCase setup stdout/stderr capture and
it is better to be used.

Change-Id: I3537a633125e5e474fda660581f41e5f57af26ca
Closes-Bug: 1262550
Merge "Corrects broken format strings in check_i18n.py"