Bug fix on `octomacs-rake-with-rvm'.

Hi jhelwig.
I found octomacs on package-list, tried it, and hit a bug.The  newest rvm.el dosen't support `rvm--rvmrc-locate' so `octomacs-rake-with-rvm' need some changes. Also I found `octomacs-unit-test-octomacs-format-rake-task-with-args-with-single-arg' failed and implemented it.
This pull-request
o Fixes the bug on `octomacs-rake-with-rvm'
o Changes the test case to fit the bug fixment
o Implements `octomacs-format-rake-task-with-args' with a single non-list args.
Please merge this if all the tests pass on your machine.