Give less scary error messages when a containerised command fails

This affects errors encountered at build time and at system-integration time.

New errors look like this:

    ERROR: Command failed: baserock/system-integration/02-install-gerrit-gerrit-installation-binaries-misc-0000:
    Containerisation settings: {'mounts': (('dev/shm', 'tmpfs', 'none'), ('tmp', 'tmpfs', 'none')), 'mount_proc': True, 'root': '/var/tmp/staging/tmp1YQ2yN/minimal-system-x86_64-generic.inst'}
    Error output:
    + install -D /usr/share/gerrit/gerrit-2.9.war /home/gerrit2/gerrit/gerrit-2.9.war -o gerrit2 -g gerrit2 -m 644
    install: can't change ownership of /home/gerrit2/gerrit/gerrit-2.9.war: Operation not permitted

Previously the error message would have been this:

    Command failed: unshare --mount -- sh -ec.
    mount --make-rprivate /
    root="$1"
    shift
    while true; do
        case "$1" in
        --)
            shift
            break
            ;;
        *)
            mount_point="$1"
            mount_type="$2"
            mount_source="$3"
            shift 3
            path="$root/$mount_point"
            mount -t "$mount_type" "$mount_source" "$path"
            ;;
        esac
    done

    exec "$@"
     - /var/tmp/staging/tmppeA1Iw/gerrit-x86_64.inst/ dev/shm tmpfs none tmp tmpfs none -- linux-user-chroot --chdir . --mount-proc proc
    /var/tmp/staging/tmppeA1Iw/gerrit-x86_64.inst/ baserock/system-integration/02-install-gerrit-gerrit-installation-binaries-misc-0000
    + install -D /usr/share/gerrit/gerrit-2.9.war /home/gerrit2/gerrit/gerrit-2.9.war -o gerrit2 -g gerrit2 -m 644
    install: can't change ownership of /home/gerrit2/gerrit/gerrit-2.9.war: Operation not permitted

1 files changed, 26 insertions, 15 deletions

diff --git a/morphlib/stagingarea.py b/morphlib/stagingarea.py
index b676d4db..7060382a 100644
--- a/morphlib/stagingarea.py
+++ b/morphlib/stagingarea.py
@@ -274,22 +274,33 @@ class StagingArea(object):
         else:
             binds = ()
 
+        container_config=dict(
+            cwd=kwargs.pop('cwd', '/'),
+            root=chroot_dir,
+            mounts=self.to_mount,
+            binds=binds,
+            mount_proc=mount_proc,
+            writable_paths=do_not_mount_dirs)
+
         cmdline = morphlib.util.containerised_cmdline(
-                    argv, cwd=kwargs.pop('cwd', '/'),
-                    root=chroot_dir, mounts=self.to_mount,
-                    binds=binds, mount_proc=mount_proc,
-                    writable_paths=do_not_mount_dirs)
-        try:
-            if kwargs.get('logfile') != None:
-                logfile = kwargs.pop('logfile')
-                teecmd = ['tee', '-a', logfile]
-                return self._app.runcmd(cmdline, teecmd, **kwargs)
-            else:
-                return self._app.runcmd(cmdline, **kwargs)
-        except cliapp.AppException as e:
-            raise cliapp.AppException('In staging area %s: running '
-                                      'command \'%s\' failed.' % 
-                                      (self.dirname, ' '.join(argv)))
+            argv, **container_config)
+
+        if kwargs.get('logfile') != None:
+            logfile = kwargs.pop('logfile')
+            teecmd = ['tee', '-a', logfile]
+            exit, out, err = self._app.runcmd_unchecked(
+                cmdline, teecmd, **kwargs)
+        else:
+            exit, out, err = self._app.runcmd_unchecked(cmdline, **kwargs)
+
+        if exit == 0:
+            return out
+        else:
+            logging.debug('Command returned code %i', exit)
+            msg = morphlib.util.error_message_for_containerised_commandline(
+                argv, err, container_config)
+            raise cliapp.AppException(
+                'In staging area %s: %s' % (self.dirname, msg))
 
     def abort(self): # pragma: no cover
         '''Handle what to do with a staging area in the case of failure.