contint: extract android SDK dependencies to a module

The Android SDK requires a few specific packages and ant 1.8+.  It is
being used by other projects than contint (ex: on Tools Labs) so this is
factoring out the code to a new androidsdk module.

* creates module androidsdk
* get rid of contint::android-sdk, moved to androidsdk::dependencies
* Tools Labs might want the packages to be ensure => latest, so have the
  dependency class to accept a different ensure value for packages it
  defines.
* be paranoid and only define Package['ant'] when it is not there already.
* remove obsolete ant18 class since Ubuntu Precise ship ant 1.8 by
  default
* Move out android SDK include from gallium in favor of an include in
  contint::packages (one less line in site.pp).

Change-Id: Ic37af0fd68fbabe0c8defbdc865364e142118290