Introduce Asterisk_Tests testsuite

Add initial infrastructure to run tests against an Asterisk process.
An not-yet-finished draft test doing registration is submitted to
validate communication towards Asterisk works.

The testsuite will be improved in follow-up commits, but this way other
people can already start using it and we can set up the dockerized setup
+ jenkins jobs to run it nightly.

Related: SYS#6782
Change-Id: I66f776d5df6fb5dc488d9e589b84a6b2385406e8
diff --git a/Makefile b/Makefile
index 51e51ed..bd88ca5 100644
--- a/Makefile
+++ b/Makefile
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 SUBDIRS= \
+	asterisk \
 	bsc \
 	bsc-nat \
 	bts \