Change check_install to take an list of parameters instead of a string.
The check_install method is used to check to see if various command-line

tools we use are present. This method used to take a string and split it on

spaces to get a list of parameters. This seemed an ugly and error-prone way of

breaking things up, so I've changed it to take in a list of parameters instead,

which are passed directly into Popen.

Ran unit tests.
Smoke tested rbt.