Use java.nio to manage files

Use java.nio to manage files

It remains several places (mainly in test-common module) where files are
handled with the java.io package.
Instead, use the more modern objects from java.nio.file.
Also, use Files.newBufferedReader() instead of FileReader.

JIRA: TRNSPRTPCE-854
Change-Id: I9abb07071e4e7e4150d03c07146fbebf09691451
Signed-off-by: Gilles Thouenon <gilles.thouenon@orange.com>