refactor env handling for FDroidPopen to support .fdroid.* metadata

The start up sequence of processes that are based on the .fdroid.* metadata
is a bit different, so this ensures that the environment variables get
properly initialized in all cases.

This also creates a single function where the environment is set.  Before
it was being set in multiple places across multiple files.

tests/common.TestCase

@@ -64,7 +64,7 @@ class CommonTest(unittest.TestCase):
 
     def testIsApkDebuggable(self):
         config = dict()
-        config['sdk_path'] = os.getenv('ANDROID_HOME')
+        fdroidserver.common.fill_config_defaults(config)
         fdroidserver.common.config = config
         self._set_build_tools()
         config['aapt'] = fdroidserver.common.find_sdk_tools_cmd('aapt')

tests/import.TestCase

@@ -25,8 +25,9 @@ class ImportTest(unittest.TestCase):
 
     def test_import_gitlab(self):
         # FDroidPopen needs some config to work
-        fdroidserver.common.config = dict()
-        fdroidserver.common.config['sdk_path'] = '/fake/path/to/android-sdk'
+        config = dict()
+        fdroidserver.common.fill_config_defaults(config)
+        fdroidserver.common.config = config
 
         url = 'https://gitlab.com/fdroid/fdroidclient'
         app = fdroidserver.metadata.get_default_app_info()

tests/install.TestCase

@@ -23,7 +23,7 @@ class InstallTest(unittest.TestCase):
 
     def test_devices(self):
         config = dict()
-        config['sdk_path'] = os.getenv('ANDROID_HOME')
+        fdroidserver.common.fill_config_defaults(config)
         fdroidserver.common.config = config
         config['adb'] = fdroidserver.common.find_sdk_tools_cmd('adb')
         self.assertTrue(os.path.exists(config['adb']))

tests/update.TestCase

@@ -29,6 +29,10 @@ class UpdateTest(unittest.TestCase):
         if not os.path.exists(getsig_dir + "/getsig.class"):
             logging.critical("getsig.class not found. To fix: cd '%s' && ./make.sh" % getsig_dir)
             sys.exit(1)
+        # FDroidPopen needs some config to work
+        config = dict()
+        fdroidserver.common.fill_config_defaults(config)
+        fdroidserver.common.config = config
         p = FDroidPopen(['java', '-cp', os.path.join(os.path.dirname(__file__), 'getsig'),
                          'getsig', os.path.join(os.getcwd(), apkfile)])
         sig = None