test/run_tests: Always set paths when OPENSSL_ROOT_DIR is defined

When the environment variable OPENSSL_ROOT_DIR is defined, we need to
ensure that PATH and LD_LIBRARY_PATH are properly affected.

This is a little bit complicated, since OPENSSL_ROOT_DIR could point
at an OpenSSL build directory as well as an OpenSSL installation
tree.  Fortunately, it's easy to detect the difference; if it's a
build tree, there's a sub-directory 'apps'.

For installation trees, it's further complicated by OpenSSL's
'multilib' target attribute, which exists for platforms that support
directory separated libraries for differing bitness (typically 32-bit
and 64-bit libraries).  We trust pkg-config to give us the answer.
Binaries are easier, they live in $OPENSL_ROOT_DIR/bin.

Fixes #146