Use syscall.Exec in installcommand
Use syscall.Exec in installcommand

I noticed something inefficient regarding the process tree:

    - init
        - installcommand (symlinked from rush)
            - rush
	        - installcommand (symlinked from ps)
	            - ps

`init` is PID 1. `installcommand` is `init`'s child. `rush` is
`installcommand`'s child. Etc...

By using syscall.Exec in installcommand, the tree is simplified to what
you would expect:

    - init
        - rush
	    - ps

This will likely make process control easier because a process's
children are always its children regardless of being run through
`installcommand`. Features like `CTRL-C`, `CTRL-Z`, and `&` should be
easier to implement.

Signed-off-by: Ryan O'Leary <32139beaa9c574695821e85473b09a4e33316467@google.com>

rminnich/u-root,u-root/u-root,rminnich/u-root,GanShun/u-root,hugelgupf/u-root,rminnich/u-root,rminnich/u-root,GanShun/u-root,hugelgupf/u-root,hugelgupf/u-root,hugelgupf/u-root,u-root/u-root,GanShun/u-root,u-root/u-root