Move some android platform functions to lldbplatformutil.

My eventual goal is to move all of the test decorators to their
own module such as `decorators.py`.  But some of the decorators
use existing functions in `lldbtest.py` and conceptually the
functions are probably more appropriately placed in lldbplatformutil.
Moreover, lldbtest.py is a huge file with a ton of random utility
functions scattered around, so this patch also workds toward the
goal of reducing the footprint of this one module to a more
reasonable size.

So this patch moves some of them over to lldbplatformutil with the
eventual goal of moving decorators over to their own module.

Reviewed By: Tamas Berghammer, Pavel Labath
Differential Revision: http://reviews.llvm.org/D16830

llvm-svn: 259680