gather: Load JSON mapping relative to config dir

JIRA: RHELCMP-7195
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

doc/configuration.rst

@@ -911,7 +911,8 @@ Options
 **gather_source_mapping**
     (*str*) -- JSON mapping with initial packages for the compose. The value
     should be a path to JSON file with following mapping: ``{variant: {arch:
-    {rpm_name: [rpm_arch|None]}}}``.
+    {rpm_name: [rpm_arch|None]}}}``. Relative paths are interpreted relative to
+    the location of main config file.
 
 **gather_profiler** = False
     (*bool*) -- When set to ``True`` the gather tool will produce additional

pungi/phases/gather/sources/source_json.py

@@ -32,6 +32,7 @@ set([(rpm_name, rpm_arch or None)])
 
 
 import json
+import os
 
 import pungi.phases.gather.source
 
@@ -41,7 +42,7 @@ class GatherSourceJson(pungi.phases.gather.source.GatherSourceBase):
         json_path = self.compose.conf.get("gather_source_mapping")
         if not json_path:
             return set(), set()
-        with open(json_path, "r") as f:
+        with open(os.path.join(self.compose.config_dir, json_path), "r") as f:
             mapping = json.load(f)
 
         packages = set()