Issues with configure option --with-openssl=PATH

[bjosv]

When building with a specific OpenSSL installation using
./configure --with-crypto-backend=openssl --with-openssl=<path>
the given path will not be verified if it is a valid OpenSSL installation.

If the path is not valid configure will instead search and possibly find the system installed OpenSSL instead, without notifying the user.

checking what are the OpenSSL includes... -I/home/bjorn/tmp/invalid-openssl-dir/include
checking what are the OpenSSL libs... -L/home/bjorn/tmp/invalid-openssl-dir/lib -lcrypto
checking for openssl/ssl.h... yes

An additional problem exist when running configure with a correctly installed OpenSSL in an alternative path.
When the tests are built the linker is not given the RPATH to the expected OpenSSL path,
which means that the system installed OpenSSL libraries are used when the tests are run.

A CMake build does this correctly though, as in following example:

cmake -DBUILD_TESTS=ON -DOPENSSL_ROOT_DIR=/home/bjorn/tmp/openssl-1.1.1w ..

ldd ./src/lib/slot_mgr/test/slotmgrtest
	linux-vdso.so.1 (0x00007fff651d5000)
	libcrypto.so.1.1 => /home/bjorn/tmp/openssl-1.1.1w/lib/libcrypto.so.1.1 (0x00007f61cec00000)