Tests for TRACE requests should not send/expect body

[mekras]

Q	A
Bug?	probably
New Feature?	no
Version	0.5.1

According to RFC7231:

A client MUST NOT send a message body in a TRACE request.

But some data sets provided by HttpBaseTest::requestProvider contain body for TRACE requests.

[kelunik]

Didn't see this issue before, solved via #29.