test: unit/crypto.test flaky fails

[Totktonada]

Tarantool version: 2.2.0-465-g88a232903 Linux-x86_64-Debug.
OS version: Gentoo Linux.

Reproduced by Travis-CI and locally:

TEST_RUN_TESTS="$(yes unit/crypto.test | head -n 1000)" make test

[011] Test failed! Result content mismatch:
[011] --- unit/crypto.result	Sat Jun 22 18:46:06 2019
[011] +++ unit/crypto.reject	Sun Jun 23 18:50:16 2019
[011] @@ -1,3 +1,9 @@
[011] +    #   Failed test 'decrypt can fail with wrong IV'
[011] +    #   in /home/alex/p/tarantool-meta/r/t-2/test/unit/crypto.c at line 92
[011] +    # Looks like you failed 1 test of 20 run.
[011] +#   Failed test 'subtests'
[011] +#   in /home/alex/p/tarantool-meta/r/t-2/test/unit/unit.c at line 54
[011] +# Looks like you failed 1 test of 5 run.
[011]  	*** main ***
[011]  1..5
[011]  ok 1 - crypto checks that algo argument is correct
[011] @@ -15,7 +21,7 @@
[011]      ok 10 - decrypt also checks length and returns needed number of bytes
[011]      ok 11 - decrypt returns correct number of bytes
[011]      ok 12 - and correctly decrypts data
[011] -    ok 13 - decrypt can fail with wrong IV
[011] +    not ok 13 - decrypt can fail with wrong IV
[011]      ok 14 - diag error is set
[011]      ok 15 - encrypt with different IV and the same number of written bytes returned
[011]      ok 16 - the encrypted data looks different
[011] @@ -23,7 +29,7 @@
[011]      ok 18 - data is the same
[011]      ok 19 - encrypt with one codec, but decrypt with another codec and the same key
[011]      ok 20 - data is the same
[011] -ok 2 - subtests
[011] +not ok 2 - subtests
[011]  	*** test_aes128_codec: done ***
[011]  	*** test_aes128_stress ***
[011]      1..1

[Gerold103]

Seems like sometimes crypto_codec_gen_iv generates such an IV, that it causes not decryption error with a different IV, but just a wrong decryption. Probably that test should be just dropped.