Support identifying different tgz files based on run_label attribute

tgz files in trials can be categorized in subdirectories, allowing to
select different bianry files at runtime based on the target run node
which is going to run them. This way for instance one can have a binary
linked against libs for eg. CentOS under run_label "centos/" or an ARM
target under "arm", and then use "run_label: arm" on the resource using
it.

Change-Id: Iaf2e97da3aff693395f44f0e93b184d4846cf6da
diff --git a/.gitignore b/.gitignore
index ad9b423..ff09035 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,13 +4,16 @@
 .version
 _version.py
 tags
-set_pythonpath
-test_work
 state
 *.pyc
 sysmocom/resources.conf
 sysmocom/ttcn3/resources.conf
 
+# selftest:
+set_pythonpath
+test_work
+selftest/trial_test/run_label/inst/
+
 # manuals
 doc/manuals/*.html
 doc/manuals/*.svg