releasetools: Add compatibility for custom out directory.

sign_target_files_apks script looks for the signapk.jar inside the out dir.
If the our dir is set to a different directory via OUT_DIR_COMMON_BASE the script does not work properly.

From now script checks if the OUT_DIR_COMMON_BASE is set, then searches the jar in the proper path.
If OUT_DIR_COMMON_BASE is unset, searches in "out" like it did before.

Test: Build with OUT_DIR_COMMON_BASE set and unset and verify that sign_target_files_apks works in both cases

Change-Id: I9218b98ff79526184f8353705640193405afac9e
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index cfa81e1..9cda0bd 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -46,9 +46,15 @@
 
 class Options(object):
   def __init__(self):
+    base_out_path = os.getenv('OUT_DIR_COMMON_BASE')
+    if base_out_path is None:
+      base_search_path = "out"
+    else:
+      base_search_path = os.path.join(base_out_path, os.path.basename(os.getcwd()))
+
     platform_search_path = {
-        "linux2": "out/host/linux-x86",
-        "darwin": "out/host/darwin-x86",
+        "linux2": os.path.join(base_search_path, "host/linux-x86"),
+        "darwin": os.path.join(base_search_path, "host/darwin-x86"),
     }
 
     self.search_path = platform_search_path.get(sys.platform)