Fixed disabling of ls color output

First patch fixes problems with ls color output on Ubuntu 12.04 and makes 'unset LS_COLORS' redundant.
These patches solve issues #147 and #149. Second patch is just to make the code cleaner. If it breaks Mac OS it can be dropped. Setting shell=False is enough to fix this issue on Linux

My guess is that problems are caused by different default parameters for 'local' and 'run' fabric functions. 'local' by default uses shell=False and 'run' uses shell=True.

I have no access to Mac OS so I am unable to test it. Maybe somebody can test it on Mac.