tests: use -no-install libtool flag to avoid ./lt-* scripts

This ensures that the rpath of the generated binaries is set to
use only the just-compiled libosmo{core,gsm,vty}.so and not any
system-wide installed libraries while avoiding the ugly shell script
wrapper.

Change-Id: I9b9ae0ed277ba71519661a66a70b7f86971e4511
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 63f3959..ab3728f 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -1,6 +1,6 @@
 AM_CPPFLAGS = -I$(top_srcdir)/include -I$(top_builddir)/include
 AM_CFLAGS = -Wall $(TALLOC_CFLAGS)
-AM_LDFLAGS =
+AM_LDFLAGS = -no-install
 LDADD = $(top_builddir)/src/libosmocore.la $(TALLOC_LIBS)
 
 if ENABLE_SERCOM_STUB