This patch removes pkg/util/mount completely, and replaces it with the
mount package now located at k8s.io/utils/mount. The code found at
k8s.io/utils/mount was moved there from pkg/util/mount, so the code is
identical, just no longer in-tree to k/k.
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.
We were not sorting them previously, which made the order
non-deterministic. If we believe the order doesn't matter, let's pick
a consistent order to minimize the chances of a rare flake.
This also simplifies the unit tests, which were flaking
not-very-rarely, e.g. with
`bazel test //pkg/volume/awsebs/... --runs_per_test=8`
