HPCC-8506 Implement SecureSocket::readtms to support HTTPS SOAPCALL

Previously SOAPCALL over HTTPS would fail because SecureSocket
did not implement the readtms method of the ISocket interface.

Signed-off-by: Anthony Fishbeck <Anthony.Fishbeck@lexisnexis.com>
Merge pull request #3824 from afishbeck/soapcall_https8506

HPCC-8506 Implement SecureSocket::readtms to support HTTPS SOAPCALL

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>