target: read_tree_values: handle multiline values

Extend Target.read_tree_values() to handle notes that contain line
breaks in their values. Underlying this method, is a call to

	grep -r '' /tree/root/

When files under that location contain multiple lines, grep will output
each line prefixed with the path; e.g. a file "test" with the contents
"one\n\ntwo\n" will be output by grep as:

	/tree/root/test: one
	/tree/root/test:
	/tree/root/test: two

Previous implementation of read_tree_values() was assuming one value per
line, and that the paths were unique. Since it wasn't checking for
duplicate paths, it would simply override the earlier entries resulting
with the value of "two" for test.

This change ensure that such multiline values are now handled correctly,
and the entire value is preserved.

To keep compatibility with existing uses of read_tree_values(), the
trailing new lines are stripped.

devlib/target.py

@@ -24,7 +24,7 @@ import tarfile
 import tempfile
 import threading
 import xml.dom.minidom
-from collections import namedtuple
+from collections import namedtuple, defaultdict
 
 from devlib.host import LocalConnection, PACKAGE_BIN_DIRECTORY
 from devlib.module import get_module
@@ -676,12 +676,15 @@ class Target(object):
         command = 'read_tree_values {} {}'.format(path, depth)
         output = self._execute_util(command, as_root=self.is_rooted,
                                     check_exit_code=check_exit_code)
-        result = {}
+
+        accumulator = defaultdict(list)
         for entry in output.strip().split('\n'):
             if ':' not in entry:
                 continue
             path, value = entry.strip().split(':', 1)
-            result[path] = value
+            accumulator[path].append(value)
+
+        result = {k: '\n'.join(v).strip() for k, v in accumulator.items()}
         return result
 
     def read_tree_values(self, path, depth=1, dictcls=dict, check_exit_code=True):

tests/test_target.py

@@ -0,0 +1,32 @@
+import os
+import shutil
+import tempfile
+from unittest import TestCase
+
+from devlib import LocalLinuxTarget
+
+
+class TestReadTreeValues(TestCase):
+
+    def test_read_multiline_values(self):
+        data = {
+            'test1': '1',
+            'test2': '2\n\n',
+            'test3': '3\n\n4\n\n',
+        }
+
+        tempdir = tempfile.mkdtemp(prefix='devlib-test-')
+        for key, value in data.items():
+            path = os.path.join(tempdir, key)
+            with open(path, 'w') as wfh:
+                wfh.write(value)
+
+        t = LocalLinuxTarget(connection_settings={'unrooted': True})
+        raw_result = t.read_tree_values_flat(tempdir)
+        result = {os.path.basename(k): v for k, v in raw_result.items()}
+
+        shutil.rmtree(tempdir)
+
+        self.assertEqual({k: v.strip()
+                          for k, v in data.items()},
+                         result)