ssl: store socket in setEmptyDefaultConfiguration

The setEmptyDefaultConfiguration test creates a socket and connects its
sslErrors signal to tst_QSslSocket's ignoreErrorSlot slot. This slot
expects the socket to have been stored in tst_QsslSocket's "socket"
member, which was not being done. This patch fixes this problem.

It does beg the question of whether having a "socket" member in the
tst_QSslSocket class is a good idea as it is error prone.

Change-Id: Ic59d1789c5f1ed240c3f0c37981f6ecc35572f0d
Reviewed-by: Richard J. Moore <rich@kde.org>