cryptohome: Move stateless wrapper functions out of CryptohomeLibrary

These functions don't have to be in CryptohomeLibrary. If you need to
avoid real D-Bus method calls (ex. in tests), you can use
FakeCryptohomeClient.

BUG=141016
TEST=none
R=hashimoto@chromium.org, pneubeck@chromium.org

Review URL: https://codereview.chromium.org/24869003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226373 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226373