ssh-add should print error message when it fails

[Karl-Philipp Richter]

Currently only the case when the key password is wrong is covered (with an error message), otherwise the user has to check `echo $?` to figure out that the key hasn't been added and very likely assumes that it has been.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: openssh-client 1:6.7p1-5ubuntu1
Uname: Linux 4.0.1-040001-generic x86_64
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Fri May 1 18:36:37 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-04-02 (28 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Beta amd64 (20150326)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
RelatedPackageVersions:
 ssh-askpass N/A
 libpam-ssh N/A
 keychain N/A
 ssh-askpass-gnome 1:6.7p1-5ubuntu1
SSHClientVersion: OpenSSH_6.7p1 Ubuntu-5ubuntu1, OpenSSL 1.0.1f 6 Jan 2014
SourcePackage: openssh
SystemImageInfo:
 current build number: 0
 device name:
 channel: daily
 last update: Unknown
UpgradeStatus: No upgrade log present (probably fresh install)

[Rolf Leggewie (r0lf)]

Can you elaborate on a test case?

[Launchpad Janitor (janitor)]

[Expired for openssh (Ubuntu) because there has been no activity for 60 days.]