test-pattern: substitute common compression list

The compression list as to be matched with a glob because zstd might not be part
of the option. By using a substitution for these, we won't have to re-glob them
over and over.

tests/common-pattern.py

@@ -0,0 +1,9 b''
+# common patterns in test at can safely be replaced
+from __future__ import absolute_import
+
+substitutions = [
+    # list of possible compressions
+    (br'zstd,zlib,none,bzip2',
+     br'$USUAL_COMPRESSIONS$'
+    ),
+]