Additional changes to temporarily enable running tests:
ssl_srv.c and test_suite_ecdh use mbedtls_ecp_group_load instead of
mbedtls_ecdh_setup
test_suite_ctr_drbg uses mbedtls_ctr_drbg_update instead of
mbedtls_ctr_drbg_update_ret
The ECJPAKE test suite uses a size zero array for the empty password
used in the tests, which is not valid C. This commit fixes this.
This originally showed up as a compilation failure on Visual Studio
2015, documented in IOTSSL-1242, but can also be observed with GCC
when using the -Wpedantic compilation option.
