Introduce contrib/jenkins-build-amarisoft.sh

Prepares inst tgz archives to be consumed by osmo-gsm-tester from
Amarisoft prebuilt binaries.

Change-Id: I372606fc5ff9f6bb3ef848f2fe229b83382ddc09
diff --git a/src/osmo_gsm_tester/amarisoft_enb.py b/src/osmo_gsm_tester/amarisoft_enb.py
index 79b90a7..5b4e99e 100644
--- a/src/osmo_gsm_tester/amarisoft_enb.py
+++ b/src/osmo_gsm_tester/amarisoft_enb.py
@@ -82,7 +82,9 @@
 
     def bin_prefix(self):
         if self._bin_prefix is None:
-            self._bin_prefix = os.getenv('AMARISOFT_PATH_ENB', AmarisoftENB.REMOTE_DIR)
+            self._bin_prefix = os.getenv('AMARISOFT_PATH_ENB', None)
+            if self._bin_prefix == None:
+                self._bin_prefix  = self.suite_run.trial.get_inst('amarisoftenb')
         return self._bin_prefix
 
     def cleanup(self):