Add Scientific Linux boxes

[treydock]

Pull Requests coming for Scientific Linux 6.4 x64 using Virtualbox. Once I get a copy of Fusion I can build those also.

Basing the 'nocm' version off the CentOS 6.4 x64 nocm, I was unable to make "validate" pass the ruby and gem checks. I assume this is expected, and was unable to find documented methods for skipping those validations unless I use the 2nd example below.

$ veewee vbox validate scientific-64-x64-vb4210-nocm --tags=vagrant virtualbox
Checking user - OK
Checking sudo - OK
Checking ruby - FAILED
Command: . /etc/profile ;ruby --version 2> /dev/null 1> /dev/null;  echo $?
Expected string 0
Output:
Checking gem - FAILED
Command: . /etc/profile ;gem --version 2> /dev/null 1> /dev/null;  echo $?
Expected string 0
Output:
Checking shared folder - OK

$ veewee vbox validate scientific-64-x64-vb4210-nocm --tags=vagrant
Checking shared folder - OK

[treydock]

See #17 , didn't mean to create duplicate once PR was opened.