Check more errors in OpenSSL crypto backend

In krb5int_hmac_keyblock() and krb5int_pbkdf2_hmac(), check for errors
from previously unchecked OpenSSL function calls and return
KRB5_CRYPTO_INTERNAL if they fail.

HMAC_Init() is deprecated in OpenSSL 1.0 and later; as we are
modifying the call to check for errors, call HMAC_Init_ex() instead.

https://github.com/krb5/krb5/commit/2298e5c2ff1122bcaff715129f5b746e77c3f42a
Author: Greg Hudson <ghudson@mit.edu>
Commit: 2298e5c2ff1122bcaff715129f5b746e77c3f42a
Branch: master
 src/lib/crypto/openssl/hmac.c   |   18 +++++++++---------
 src/lib/crypto/openssl/pbkdf2.c |    9 +++++----
 2 files changed, 14 insertions(+), 13 deletions(-)