Don't run the tests in parallel.

Only run test-python when testing in the python3 sub-build.

nbdkit.spec

@@ -368,19 +368,21 @@ mkdir -p $HOME/.cache/libvirt
 export LIBGUESTFS_DEBUG=1
 export LIBGUESTFS_TRACE=1
 
-# Unlikely that libguestfs will work on ARM and PPC, so don't try running the
-# tests there.
-# Broken on i686 because of https://bugzilla.redhat.com/show_bug.cgi?id=1302071
+# Disabled on armv7 and ppc/power because we haven't currently spent
+# any effort on making the tests work there.
+#
+# The tests rely on libguestfs which needs the kernel to work, and that
+# usually doesn't work on i686, so it is disabled.
 %ifnarch %{arm} %{ix86} ppc %{power64}
 
-make check || {
+make check -j1 || {
     cat tests/test-suite.log
     exit 1
   }
 
 %if 0%{?have_python3}
 pushd python3
-make check || {
+make check -j1 TESTS=test-python || {
     cat tests/test-suite.log
     exit 1
   }