INSTALL.Windows: Add details about local build and installation.

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.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Nithin Raju <nithin@vmware.com>