Added DateUtility.formatNanos() method (incl. JUnit tests)

Change-Id: I2fc6785e0b2194bc56ee2c38ef9d0e1451f0f1bc
Reviewed-on: https://git.eclipse.org/r/38431
Tested-by: Hudson CI
Reviewed-by: Claudio Guglielmo <claudio.guglielmo@bsiag.com>