Remove references to top_sourcedir in Makefile.am

I don't know why, but this was necessary, and all the other tests does
this. I was getting the following errors after enabling subdir-objects
in `AM_INIT_AUTOMAKE`:

```
Makefile:1843: ../../cf-upgrade/.deps/cf_upgrade_test-alloc-mini.Po: No such file or directory
Makefile:1844: ../../cf-upgrade/.deps/cf_upgrade_test-command_line.Po: No such file or directory
Makefile:1845: ../../cf-upgrade/.deps/cf_upgrade_test-configuration.Po: No such file or directory
Makefile:1846: ../../cf-upgrade/.deps/cf_upgrade_test-log.Po: No such file or directory
Makefile:1847: ../../cf-upgrade/.deps/cf_upgrade_test-process.Po: No such file or directory
Makefile:1848: ../../cf-upgrade/.deps/cf_upgrade_test-update.Po: No such file or directory
```

Ticket: CFE-2780
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

tests/unit/Makefile.am

@@ -381,17 +381,17 @@ verify_databases_test_LDADD = ../../cf-agent/libcf-agent.la libtest.la
 iteration_test_SOURCES = iteration_test.c
 
 cf_upgrade_test_SOURCES = cf_upgrade_test.c \
-	$(top_srcdir)/cf-upgrade/alloc-mini.c \
-	$(top_srcdir)/cf-upgrade/alloc-mini.h \
-	$(top_srcdir)/cf-upgrade/command_line.c \
-	$(top_srcdir)/cf-upgrade/command_line.h \
-	$(top_srcdir)/cf-upgrade/configuration.c \
-	$(top_srcdir)/cf-upgrade/configuration.h \
-	$(top_srcdir)/cf-upgrade/log.c $(top_srcdir)/cf-upgrade/log.h \
-	$(top_srcdir)/cf-upgrade/process.c $(top_srcdir)/cf-upgrade/process.h \
-	$(top_srcdir)/cf-upgrade/update.c \
-	$(top_srcdir)/cf-upgrade/update.h
-cf_upgrade_test_CPPFLAGS = -I$(top_srcdir)/cf-upgrade -I$(top_srcdir)/libntech/libutils -I$(top_srcdir)
+	../../cf-upgrade/alloc-mini.c \
+	../../cf-upgrade/alloc-mini.h \
+	../../cf-upgrade/command_line.c \
+	../../cf-upgrade/command_line.h \
+	../../cf-upgrade/configuration.c \
+	../../cf-upgrade/configuration.h \
+	../../cf-upgrade/log.c ../../cf-upgrade/log.h \
+	../../cf-upgrade/process.c ../../cf-upgrade/process.h \
+	../../cf-upgrade/update.c \
+	../../cf-upgrade/update.h
+cf_upgrade_test_CPPFLAGS = -I../../cf-upgrade -I../../libntech/libutils -I../../
 cf_upgrade_test_LDADD = libtest.la ../../libntech/libcompat/libcompat.la
 
 if !NT