Switch popen.wait() for popen.communicate() (#332)
Switch popen.wait() for popen.communicate() (#332)

wait() can hang if there is too much to read (buffer fills before command
exits). communicate() will do all the reading for us.

Fixes issue #330
mit-ll/python-keylime,mit-ll/python-keylime,mit-ll/python-keylime,mit-ll/python-keylime