Add a test to check that RAND_bytes_ex() works with a child lib ctx
Add a test to check that RAND_bytes_ex() works with a child lib ctx

Previously, when locks were held while calling a provider init function,
then RAND_bytes_ex() would fail if called from the init function and
used in conjunction with a child lib ctx. We add an explicit test of that.

Reviewed-by: Paul Dale <ddec78389666b4f7c9b4d110380c848489a3e4aa@openssl.org>
Reviewed-by: Tomas Mraz <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15854)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl