jenkins-slave package fails to upgrade if jenkins server is unreachable

[Jean-Baptiste Lallement]

This is a bit of a corner case but if for some reason jenkins slave is already configured and upgraded but jenkins server is unreachable, then the package upgrade hangs forever while trying to download slave.jar on start.

The process list is:
\_ /bin/sh /var/lib/dpkg/info/jenkins-slave.postinst configure 1.480.3+dfsg-1
     \_ /bin/sh /usr/sbin/invoke-rc.d jenkins-slave start
         \_ start jenkins-slave
[...]
/bin/sh -e /proc/self/fd/9
 \_ /bin/sh /usr/share/jenkins/bin/download-slave.sh http://192.168.1.4:8080
   \_ wget -q -O /var/run/jenkins/slave.jar http://192.168.1.4:8080/jnlpJars/slave.jar

download-slave.sh could check the availability of the server before trying to download slave.jar.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: jenkins (not installed)
ProcVersionSignature: Ubuntu 3.11.0-1.4-generic 3.11.0-rc4
Uname: Linux 3.11.0-1-generic x86_64
ApportVersion: 2.12-0ubuntu3
Architecture: amd64
Date: Wed Aug 14 21:47:34 2013
InstallationDate: Installed on 2012-10-25 (293 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
MarkForUpload: True
SourcePackage: jenkins
UpgradeStatus: Upgraded to saucy on 2012-12-02 (255 days ago)