Makefiles: Clean and do not distribute IDL-generated files.

Makefiles: Clean and do not distribute IDL-generated files.

IDL-generated files don't need to be distributed, and distributing them
puts them in the source directory rather than the build directory, which
causes "make distcheck" to fail if any of them need to be remade.  To
prevent this, this commit this removes them from ..._SOURCES, moving them
into nodist_..._SOURCES.

IDL-generated files all need to be cleaned, so this commit adds all of
them to CLEANFILES wholesale via a single CLEANFILES += $(OVSIDL_BUILT)
line in ovsdb/automake.mk, removing the individual additions from various
makefiles.

With this commit, "make distcheck" passes for me.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Aaron Conole <aaron@bytheb.org>