Add documentation to doc.arvados.org for the local Docker install.
Change crunch-dispatch to use "git fetch-pack --all" insted of "git fetch" to
fetch entire repository instead of just the history for HEAD.  This seems to be
the only way to ensure that arbitrary script version hashes not in the history
of the source's HEAD are fetched without using refs (tags or branches).
no issue #
UnixVolume has no business being loud about files that can not be found.
Just pass on the error to the caller and be quiet.

Back story: for every PUT, Keep checks if the block already exists.
Prior to this patch, UnixVolume would complain loudly if the block did
not already exist in the volume (i.e. the normal case for a PUT).
Move error logging for block-not-found from GetBlock to GetBlockHandler.

It doesn't belong in GetBlock because GetBlock is also called from
PutBlock, which checks to see if a block exists before it writes it
again.

In other words, in the most common scenario (a PUT of a new block), Keep
should not print a bogus error message.
Do not print an error when hitting 'not found' with a the MockVolume
backend.
Merge branch 'master' into 3141-keep-logging-improvements
Merge branch 'master' into 3141-keep-logging-improvements
Revert "Do not print an error when hitting 'not found' with a the MockVolume"

This reverts commit 97c9b2b49f94735c6d4d5b62b772089ef7e0e3bf.

Better solution in the next commit.
keep: MockVolume should return os.ErrNotExist instead of errors.New("not
found") when a block can not be found, just like a real volume.
Merge branch '3141-keep-logging-improvements'

This closes #3141