trace-cmd build: If swig is not installed, force NO_PYTHON=1

While trying to build trace-cmd on a box without swig installed, I get an
annoying error during build when the compile tries to build the python
plugins. Force NO_PYTHON=1 when swig is not installed, and give a warning
about it.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
1 file changed