vold: const-ify some of the API

We make some of the C++ member functions 'const', to reflect how
they (don't) affect the state of the class.

Test: TreeHugger
Change-Id: Iec1c2801bfe721e2741406ed1ac0ef95662840a6
Merged-In: Iec1c2801bfe721e2741406ed1ac0ef95662840a6
8 files changed