release_tarball: select the "v" tags for cephver

By default, Jenkins' Git plugin adds its own tag to the repository. This
interferes with the versioning in release_tarball.sh

One solution would be to disable the tag in the Jenkins job. Since this
is not the default, that tag creation option would need to be manually
disabled for every job in Jenkins that runs this script. The other
option is to make the script more selective about what it considers to
be cephver. This commit implements this option.

Use a --match selector to "git describe" so that we're sure we're using
the standard "vX.X" tags.

Pipe "git describe" through "sed" instead of "cut", so that it's easier
to debug what tag was selected.

Signed-off-by: Ken Dreyer <ken.dreyer@inktank.com>
Merge pull request #3 from kdreyer-inktank/jenkins

jenkins: use in-tree clone for the ceph-build repo
Merge pull request #5 from kdreyer-inktank/jenkins-cephver

release_tarball: select the "v" tags for cephver

Reviewed-by: Sage Weil <sage@inktank.com>
Revert "do up force pbuilder update on build"

This reverts commit 6fcd39b06d20f3e561533d0479ae942bf80a6010.

It's true that this will be slower, but the wheezy builds are failing if
we don't do this.

(There is an apt-mirror.front.sepia.ceph.com. Maybe using that would
speed things up?)

Signed-off-by: Ken Dreyer <ken.dreyer@inktank.com>
Merge pull request #6 from kdreyer-inktank/pbuilder-update

Revert "do up force pbuilder update on build"
jenkins: show errors and fail fast during job execution

Jenkins will dynamically write the commands in its database into a
script and run it with "-x" and "-e" in order to display each step and
fail after the first step fails.

Now that our commands are stored in Git, ensure that we're doing the
same thing.

Signed-off-by: Ken Dreyer <ken.dreyer@inktank.com>