tests: Don't construct the guests in parallel.
In automake 1.13, check_DATA is now built in parallel, resulting in it trying to build 4 or 5 guests in parallel.
|@@ -96,3 +96,8 @@ guest-aux/windows-system: guest-aux/windows-system.reg|
|cp guest-aux/minimal-hive $@-t|
|hivexregedit --merge $@-t --prefix 'HKEY_LOCAL_MACHINE\SYSTEM' $<|
|mv $@-t $@|
|+# Don't construct the guests in parallel. In automake 1.13, check_DATA|
|+# was changed so it can now run in parallel, but this causes everything|
|+# to fall over on machines with limited memory.|