Free s2n rand ENGINE during cleanup
Free s2n rand ENGINE during cleanup

Openssl 1.1.0 appears to no longer do this for us at process exit.
See https://travis-ci.org/awslabs/s2n/builds/163860492

awslabs/s2n,wcs1only/s2n,alexeblee/s2n,jldodds/s2n,wcs1only/s2n,colmmacc/s2n,raycoll/s2n,colmmacc/s2n,gibson-compsci/s2n,awslabs/s2n,jldodds/s2n,raycoll/s2n,gibson-compsci/s2n,PKRoma/s2n,bpdavidson/s2n,wcs1only/s2n,jldodds/s2n,wcs1only/s2n,alexeblee/s2n,wcs1only/s2n,alexeblee/s2n,colmmacc/s2n,bpdavidson/s2n,alexeblee/s2n,alexeblee/s2n,gibson-compsci/s2n,gibson-compsci/s2n,wcs1only/s2n,gibson-compsci/s2n,raycoll/s2n,bpdavidson/s2n,PKRoma/s2n,wcs1only/s2n,alexeblee/s2n,awslabs/s2n,awslabs/s2n,jldodds/s2n,bpdavidson/s2n,jldodds/s2n,raycoll/s2n,bpdavidson/s2n,PKRoma/s2n,awslabs/s2n,wcs1only/s2n,PKRoma/s2n,colmmacc/s2n,PKRoma/s2n,gibson-compsci/s2n,colmmacc/s2n,awslabs/s2n,raycoll/s2n,PKRoma/s2n,PKRoma/s2n,PKRoma/s2n,colmmacc/s2n,bpdavidson/s2n,raycoll/s2n