Add dependency on perl (#2909)

* Add dependency on perl

The build process uses perl and also needs `Test::More`.

Some distros, e.g. CentOS, break the core Perl distribution
into separate packages, so it's possible to "have perl" but
not have all the bits one needs to build OpenSSL.

We'll just install one of ours, which comes with all of its
factory parts included.

* Remove uninformative comment

>  # Also requires make

doesn't really add any value...

var/spack/repos/builtin/packages/openssl/package.py

@@ -53,7 +53,7 @@ class Openssl(Package):
     version('1.0.1h', '8d6d684a9430d5cc98a62a5d8fbda8cf')
 
     depends_on("zlib")
-    # Also requires make and perl
+    depends_on("perl", type='build')
 
     parallel = False