The static SimpleDateFormat instance in
AbstractMockHttpServletRequestBuilder is shared across all
instances. SimpleDateFormat.format() mutates internal Calendar
state and is not thread-safe, which can produce corrupt date
strings or ArrayIndexOutOfBoundsException when tests run in
parallel.
Replace with DateTimeFormatter which is immutable and thread-safe.
Signed-off-by: Sebastien Tardif <SebTardif@ncf.ca>
