Support LibreSSL by its version output

The command-line API for LibreSSL is currently identical to OpenSSL
1.0.1.  This support is implemented in a case so any future version
distinctions can key off the features in the available implementation.

Such feature-specific support may become more important during the 3.1
development cycle where 0.9.x OpenSSL cannot handle newer features.

Signed-off-by: Josh Cepek <josh.cepek@usa.net>
Fixes: #48

easyrsa3/easyrsa

@@ -288,9 +288,12 @@ EASYRSA_PKI env-var undefined"
 	# Verify EASYRSA_OPENSSL command gives expected output
 	if [ -z "$EASYRSA_SSL_OK" ]; then
 		local val="$("$EASYRSA_OPENSSL" version)"
-		[ "${val%% *}" = "OpenSSL" ] || die "\
+		case "${val%% *}" in
+			OpenSSL|LibreSSL) ;;
+			*) die "\
 Missing or invalid OpenSSL
 Expected to find openssl command at: $EASYRSA_OPENSSL"
+		esac
 	fi
 	EASYRSA_SSL_OK=1