tests: Make make -j8 check work

In the future we should also make it so that `make check` for `tests/db`,
`tests/gss`, and `tests/kdc` first initializes all the realms and starts all
the daemons, then runs the actual checks possibly in parallel, then shuts down
the daemons.  This will require quite a bit of work, so for now we just disable
parallel make in those directories.

tests/db/Makefile.am

@@ -2,6 +2,8 @@
 
 include $(top_srcdir)/Makefile.am.common
 
+.NOTPARALLEL:
+
 noinst_DATA = krb5.conf krb5.conf-sqlite krb5.conf-db3 krb5.conf-db1 krb5.conf-lmdb
 
 noinst_SCRIPTS = have-db

tests/gss/Makefile.am

@@ -2,6 +2,8 @@
 
 include $(top_srcdir)/Makefile.am.common
 
+.NOTPARALLEL:
+
 noinst_DATA = krb5.conf new_clients_k5.conf mech
 
 SCRIPT_TESTS = check-basic check-gss check-gssmask check-context check-spnego check-ntlm check-negoex

tests/kdc/Makefile.am

@@ -1,5 +1,7 @@
 include $(top_srcdir)/Makefile.am.common
 
+.NOTPARALLEL:
+
 noinst_DATA = \
 	an2ln-db.txt \
 	kdc-tester4.json \