Docker: get tezos-node version from docker image

Tezos running in docker would not output the version with the command tezos-client --version as reported in #681 (closed) and #641 (closed)

Including the .git/ directory in the docker build context resolves this issue.

Fixes: #641 (closed) #681 (closed)

Signed-off-by: John Naulty johnnaulty@bitgo.com