[Android][Extension] Fixed getMemoryInfo to support Android 4.0 and below.

1. The original implementation uses an API avaible since API level 16. Change
   the implementation to reading file "/proc/meminfo" when the target system
   is Android 4.0 and below.
2. The spec http://device-capabilities.sysapps.org/#memory requires to return
   byte instead of KB. So change the unit to byte.