This patch moves fake.go to mount_fake.go, and follows to principle of
always returning a discrete type rather than an Interface. All callers
of "FakeMounter" are changed to instead use "NewFakeMounter()". The
FakeMounter "Log" struct member is changed to not be exported, and
instead only access through a new "GetLog()" method.
This patch adds comments to exported items that were missing them in
order to make the linter happy. Only code changes that were limited to
the scope of this package were made. There are other linting issues that
will effect callers, and that will be done a seperate patch.
