Depending on parameters the paths in a snapshot do not directly
correspond to real paths on the filesystem. Therefore, reject funcs must
use the FS interface to work correctly.
The temp files used by the packer manager are either delete after
creation (unix) or marked as delete on close (windows). Thus, no
explicit cleanup is necessary.
The retry code path did not filter `ERROR_NOT_SUPPORTED`. Just call the
original function a second time to correctly follow the low privilege
code path.
Calling `Load()` twice for an atomic variable can return different
values each time. This resulted in trying to read the security
descriptor with high privileges, but then not entering the code path to
switch to low privileges when another thread has already done so
concurrently.
Failed locking attempts were immediately retried up to three times
without any delay between the retries. If a lock file is not found while
checking for other locks, with the reworked backend retries there is no
delay between those retries. This is a problem if a backend requires a
few seconds to reflect file deletions in the file listings. To work
around this problem, introduce a short exponentially increasing delay
between the retries. The number of retries is now increased to 4. This
results in delays of 5, 10 and 20 seconds between the retries.
When the context used for a load operation is canceled, then the result
is always an error independent of whether the file could be retrieved
from the backend. Do not false positively trip the circuit breaker in
this case.
The old behavior was problematic when trying to lock a repository. When
`Lock.checkForOtherLocks` listed multiple lock files in parallel and one
of them fails to load, then all other loads were canceled. This
cancelation was remembered by the circuit breaker, such that locking
retries would fail.
The HTTP client can only retry HTTP2 requests after receiving a GOAWAY
response if it can rewind the body. As we use a custom data type,
explicitly provide an implementation of `GetBody`.
