BUILD: ssl: eliminate warning with OpenSSL 1.1.0 regarding RAND_pseudo_bytes()

BUILD: ssl: eliminate warning with OpenSSL 1.1.0 regarding RAND_pseudo_bytes()

This function was deprecated in 1.1.0 causing this warning :

  src/ssl_sock.c:551:3: warning: 'RAND_pseudo_bytes' is deprecated (declared at /opt/openssl-1.1.0/include/openssl/rand.h:47) [-Wdeprecated-declarations]

The man suggests to use RAND_bytes() instead. While the return codes
differ, it turns out that the function was already misused and was
relying on RAND_bytes() return code instead.

The patch was tested on 0.9.8, 1.0.0, 1.0.1, 1.0.2 and 1.1.0.

This fix must be backported to 1.7 and the return code check should
be backported to earlier versions if relevant.