Fix the sqlite errors of content unittests on Android
Many tests are failed due to sqlite errors on Android.
The reason is that sqlite need a temporary directory to
store internal temporary files. However, Android doesn't
have this kind of directory while Linux has /var/tmp.
To fix this, use in-memory temporary files. It also includes:
1) Add one unit test in sql unittests to reproduce this
issue for Android.
2) Remove those disabled cases for content unitests on
TEST=run_tests.py -s sql_unittests; run_test.py -s net_unittests