tag ls: print informational messages on STDERR

[thaJeztah]

Description

Steps to reproduce the issue:

$ hub-tool tag ls nginx 1> /dev/null
# no output

$ hub-tool tag ls nginx 2> /dev/null

TAG                           DIGEST                                                                     STATUS    LAST UPDATE      LAST PUSHED    LAST PULLED       SIZE
nginx:latest                  sha256:f19d295b57fdde6f71573f487b35875ca95bd23401b142eb55eeb9d887f9f5b1    active    3 weeks ago      3 weeks        17 minutes        421.2MB
nginx:stable-alpine-perl      sha256:0c85226446a083d92fbf432faee51d12933eafdcf13eb0b7d06fc465368ae908    active    2 weeks ago      2 weeks        52 minutes        124.8MB
nginx:stable-alpine           sha256:da3716611fb965f3fda1f3281882baeb2760ca8bb7317f1d22ed45e75570827b    active    2 weeks ago      2 weeks        19 minutes        64.99MB
nginx:mainline-alpine-perl    sha256:65f87cf0859fc1de79c1346ce9b7b7ecb4abb6042339a6b696fc08309453d74c    active    2 weeks ago      2 weeks        25 minutes        126.3MB
...
nginx:1.17.4                  sha256:853d4bc0c7b54167df8954c47038d55117d3f37a70afc5871f0a5b4fdcc88f9c    active    14 months ago    14 months      4 minutes         301.3MB
nginx:1.17.3-perl             sha256:0546d4e0e8d3be6edd813bcd44c768b322f6391a52181a0ab9fb302656ebe994    active    16 months ago    16 months      6 minutes         365.9MB
nginx:1.17.3                  sha256:01c59d844f52aad434414cb7fa5bbc97545c4e6ab4ddd71fbe576a8c30c351a9    active    16 months ago    16 months      7 minutes         301.2MB
nginx:1.17.3-alpine-perl      sha256:79d35becd1e08c637d828ffbc6c7252eddf1133d2beea8b158239ff82e63c520    active    16 months ago    16 months      8 minutes         105.4MB
nginx:1.17.3-alpine           sha256:8ebb6a60c8cff4db996e987b4a3b1a5842411b7953f326186ef60566eb314b50    active    16 months ago    16 months      9 minutes         52.31MB
100/325 listed, use --all flag to show all

Describe the results you received:

The informational 100/325 listed, use --all flag to show all message is printed on STDOUT.

Describe the results you expected:

The informational 100/325 listed, use --all flag to show all message should be printed on STDERR, so that users can pipe the output to other tools for scripting/processing, e.g.:

$ hub-tool tag ls nginx | awk -F' ' '{print $2}'
DIGEST
sha256:f19d295b57fdde6f71573f487b35875ca95bd23401b142eb55eeb9d887f9f5b1
...
sha256:79d35becd1e08c637d828ffbc6c7252eddf1133d2beea8b158239ff82e63c520
sha256:8ebb6a60c8cff4db996e987b4a3b1a5842411b7953f326186ef60566eb314b50
listed,

Currently, this requires the user to strip the last line, otherwise the informational message is included (see above);

$ hub-tool tag ls nginx | head -n 101 | awk -F' ' '{print $2}'

DIGEST
sha256:f19d295b57fdde6f71573f487b35875ca95bd23401b142eb55eeb9d887f9f5b1
...
sha256:79d35becd1e08c637d828ffbc6c7252eddf1133d2beea8b158239ff82e63c520
sha256:8ebb6a60c8cff4db996e987b4a3b1a5842411b7953f326186ef60566eb314b50

Output of docker hub --version:

hub-tool --version
Docker Hub Tool v0.2.0, build 0edf43a