python: Added upm directory for python modules

* Grouped UPM python modules into upm directory, for example:
      /usr/local/lib/python2.7/dist-packages/upm
    * Updated UPM example import statements
    * Removed unused RPATH statements from UPM src CMakeLists.txt,
      currently build collateral contains an explicit RPATH which
      is stripped from the install collateral.
    * Converted python examples to work on both python2 AND python3
    * Added ctest for loading examples w/python3
    * Removed returns from swig macros
    * UPM python module use will change...
        Before:
            import pyupm_dfrph
        After:
            from upm import pyupm_dfrph
            or
            import upm.pyupm_dfrph
            etc...
    * This commit fixes #468

Signed-off-by: Noel Eck <noel.eck@intel.com>

examples/python/led.py

@@ -1,3 +1,4 @@
+from __future__ import print_function
 # Author: Sarah Knepper <sarah.knepper@intel.com>
 # Copyright (c) 2015 Intel Corporation.
 #
@@ -21,14 +22,14 @@
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 import time
-import pyupm_led as led
+from upm import pyupm_led as led
 
 def main():
     # Create the Grove LED object using GPIO pin 2
     led = led.Led(2)
 
     # Print the name
-    print led.name()
+    print(led.name())
 
     # Turn the LED on and off 10 times, pausing one second
     # between transitions