opensles detection: fail required but not found
android build: don't set WITH_OPENSLES in options

WITH_OPENSLES is automatically set by find_feature
android build: set default ndk api level to 9

API level 9 is required in order build the android client with audio
support.
FindOpenSLES: removed debug message
andriod: removed unecessary config option
Merge pull request #1521 from bmiklautz/issue/1519

Android build default ndk level