Remove the use of test/run_tests in favor of 'prove'

'prove' is a well developed TAP harness program, there's no real need
to write one's own.

We do need to set certain paths properly for the appropriate 'openssl'
program to be run.  We do that with a 'prove' plugin (WrapOpenSSL.pm)
that simply amends the appropriate system environment variables, given
a number of cmake generated environment variables that indicate where
OpenSSL files reside.