crypto/x509: add cert SmartOS cert path

Fix SmartOS build that was broken in 68292290.

SmartOS pretends to be Ubuntu/Debian with respect to its SSL
certificate location.

Change-Id: I5405c6472c8a1e812e472e7301bf6084c17549d6
Reviewed-on: https://go-review.googlesource.com/2704Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/crypto/x509/root_solaris.go

@@ -6,5 +6,6 @@ package x509
 
 // Possible certificate files; stop after finding one.
 var certFiles = []string{
-	"/etc/certs/ca-certificates.crt", // Solaris 11.2+
+	"/etc/certs/ca-certificates.crt",     // Solaris 11.2+
+	"/etc/ssl/certs/ca-certificates.crt", // Joyent SmartOS
 }