ci, build/f_repos: Minor UX improvements

After Armband rework landed of top of `build/f_repos` mechanism [1],
the following minor UX improvements can also be applied to Fuel's
f_repos:
- set SHELL to "/bin/sh" (we don't use any bash-isms);
- improve "From SHA..." removal for exported patches;
- force checkout of root tag commit during clean;
- silence progress during git clone (cleaner logs);
- support git older than 1.8.4 in `make clean` (fix Armband deploy);

FIXME:
 Pass TERM as Docker env var until [2] is fixed in Docker 1.13.

v4 -> v5:
 * Moved `export TERM` to Releng, where it actually belongs [3];
 * Fixed Armband deploys fail [4] by adjusting `make clean`;

[1] https://gerrit.opnfv.org/gerrit/#/c/22791/
[2] https://github.com/docker/docker/issues/9299
[3] https://gerrit.opnfv.org/gerrit/#/c/22933/
[4] https://build.opnfv.org/ci/view/armband/job/\
    fuel-deploy-armband-baremetal-daily-master/57/consoleText

Fixes: FUEL-200

Change-Id: I80e3074f8659769e21f5b56f07c34c7a5de727bc
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/build/f_repos/README.md b/build/f_repos/README.md
index 6cc825e05..0a52fe040 100644
--- a/build/f_repos/README.md
+++ b/build/f_repos/README.md
@@ -92,3 +92,30 @@ Sub-project maintenance
 
    $ git submodule -b stable/mitaka add --name fuel-web \
      https://github.com/openstack/fuel-web.git upstream/fuel-web
+
+2. Working with remote tracking for upgrading Fuel components
+   Enable remote tracking as described above, which at `make sub` will update
+   ALL submodules (fuel-main, fuel-library, ...) to remote branch (set in
+   .gitmodules) HEAD.
+
+   * If upstream has NOT already tagged a new version, we can still work on
+     our patches, make sure they apply etc., then check for new upstream
+     changes (and that our patches still apply on top of them) by:
+
+   $ make deepclean patches-import
+
+   * If upstream has already tagged a new version we want to pick up, checkout
+     the new tag in each submodule:
+
+   $ git submodule foreach 'git checkout <newtag>'
+
+   * Once satisfied with the patch and submodule changes, commit them:
+     - enforce FUEL_TRACK_REMOTES to "yes" if you want to constatly use the
+       latest remote branch HEAD (as soon as upstream pushes a change on that
+       branch, our next build will automatically include it - risk of our
+       patches colliding with new upstream changes);
+     - stage patch changes if any;
+     - if submodule tags have been updated (relevant when remote tracking is
+       disabled, i.e. we have a stable upstream baseline), add submodules:
+
+   $ make deepclean sub && git add -f sub/*