Fix CID 1434549: Unchecked return value in test/evp_test.c

5. check_return: Calling EVP_EncodeUpdate without checking return value
(as is done elsewhere 4 out of 5 times).

Fix CID 1371695, 1371698: Resource leak in test/evp_test.c

- leaked_storage: Variable edata going out of scope leaks the storage it
points to.

- leaked_storage: Variable encode_ctx going out of scope leaks the
storage it points to

Fix CID 1430437, 1430426, 1430429 : Dereference before null check in test/drbg_cavs_test.c

check_after_deref: Null-checking drbg suggests that it
may be null, but it has already been dereferenced on all paths leading
to the check

Fix CID 1440765: Dereference before null check in test/ssltestlib.c

check_after_deref: Null-checking ctx suggests that it may be null, but
it has already been dereferenced on all paths leading to the check.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/7993)

(cherry picked from commit 760e2d60e62511a6fb96f547f6730d05eb5f47ec)