luacrypto: use openssl allocated contexts only
luacrypto: use openssl allocated contexts only

Using stack allocated EVP_MD_CTX is causing sigsev and valgrind error:

==6975== Process terminating with default action of signal 11 (SIGSEGV)
==6975==  General Protection Fault
==6975==    at 0x4B108A: EVP_PKEY_size (p_lib.c:94)
==6975==    by 0x60BC38: sign_fsign (lcrypto.c:773)
==6975==    by 0x5AFDA5: lj_BC_FUNCC (in /data/virgo/out/Debug/monitoring-agent)
==6975==    by 0x576583: lua_call (lj_api.c:1016)
==6975==    by 0x5464CB: luv_acall (utils.c:52)
==6975==    by 0x54C18B: luv_after_fs (luv_fs.c:185)
==6975==    by 0x5E987D: uv__fs_after (fs.c:176)
==6975==    by 0x5F370C: eio_finish (eio.c:860)
==6975==    by 0x5F32C5: etp_poll (eio.c:698)
==6975==    by 0x5F392B: eio_poll (eio.c:966)
==6975==    by 0x5E905C: uv_eio_want_poll_notifier_cb (uv-eio.c:51)
==6975==    by 0x5E8413: uv__async (core.c:524)
==6975==
==6975== HEAP SUMMARY:
==6975==     in use at exit: 194,498 bytes in 2,703 blocks
==6975==   total heap usage: 3,216 allocs, 513 frees, 1,073,114 bytes allocated
==6975==
==6975== LEAK SUMMARY:
==6975==    definitely lost: 1,040 bytes in 5 blocks
==6975==    indirectly lost: 8,356 bytes in 18 blocks
==6975==      possibly lost: 1,592 bytes in 8 blocks
==6975==    still reachable: 183,510 bytes in 2,672 blocks
==6975==         suppressed: 0 bytes in 0 blocks
==6975== Rerun with --leak-check=full to see details of leaked memory
==6975==
==6975== For counts of detected and suppressed errors, rerun with: -v
==6975== ERROR SUMMARY: 16 errors from 5 contexts (suppressed: 4 from 4)
Killed

Let openssl do memory allocations instead.

kans/birgo,kans/birgo,kans/birgo,kans/birgo,kans/birgo