INSTALL.Windows: Add details about local build and installation.
This commits adds the following.
* Clearly callout to set pthread-win32's dll path in $PATH
* Details about running parallel make and parallel unit tests.
* Installing Open vSwitch locally via 'make install'
* Update the steps to run the user processes by relying on
the previous 'make install'. The steps now run the daemons
in the background with the creation of a logfile and pidfile.