PATH: Use installation directory for 'PATH'
Files in the installation directory should be able to be executed
(along with their dependencies) from any directory in the file
hierarchy. Using the installation directory as the default value for
'PATH' is the most sensible way to do this.
The PATH config directive still allows other directories to be
appended to the 'PATH' variable, which is useful when there are other
directories containing modules.
Signed-off-by: Matt Fleming <matt.fleming@intel.com>