android env: Remove dependency on SDK

Currently devlib will error out if ANDROID_HOME isn't set, it looks like aapt
is the only thing it needs from what I see. If ANDROID_HOME isn't set, just get
it from the environment.

Change-Id: I9b0ea8129cf3e4feec4f7ddf08bf843733635d92
Signed-off-by: Joel Fernandes <[email protected]>
diff --git a/devlib/utils/android.py b/devlib/utils/android.py
index bd49ea4..be8b960 100644
--- a/devlib/utils/android.py
+++ b/devlib/utils/android.py
@@ -451,7 +451,15 @@
     logger.debug('Discovering ANDROID_HOME from adb path.')
     env.platform_tools = os.path.dirname(adb_full_path)
     env.android_home = os.path.dirname(env.platform_tools)
-    _init_common(env)
+    try:
+        _init_common(env)
+    except:
+        env.aapt = which('aapt')
+        if env.aapt:
+            logger.info('Using aapt: ' + env.aapt)
+        else:
+            raise RuntimeError('aapt not found, try setting ANDROID_HOME to \
+                                Android SDK or run LISA from android environment')
     return env