Allow different version of ievms.sh

[tobymackenzie]

I was attempting to install winxp 8, but it kept appearing to hang forever. I saw some suggestions to run ievms.sh directly, but that gave me the error "Syntax error: Unknown sub command 'run' specified!". Found an issue (xdissent/ievms#278) that made me realize the master version of the script requires VirtualBox 5. I can't install that on my OS. Version 0.2.1 of 'ievms.sh' works fine:

curl -s https://raw.githubusercontent.com/xdissent/ievms/v0.2.1/ievms.sh | env IEVMS_VERSIONS="8" bash

It would be nice if detection of the VirtualBox version could change @ievmsUrl to the appropriate version. Or, for a much simpler solution, a command line option could be used to change it, something like --script-version 0.2.1.