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, 7 insertions, 2 deletions

diff --git a/morphlib/app.py b/morphlib/app.py
index 930e023d..b5bcb601 100644
--- a/morphlib/app.py
+++ b/morphlib/app.py
@@ -348,7 +348,7 @@ class Morph(cliapp.Application):
             self.output.write('%s %s\n' % (timestamp, text))
             self.output.flush()
 
-    def runcmd(self, argv, *args, **kwargs):
+    def _prepare_for_runcmd(self, argv, args, kwargs):
         if 'env' not in kwargs:
             kwargs['env'] = dict(os.environ)
 
@@ -377,9 +377,14 @@ class Morph(cliapp.Application):
         morphlib.util.log_environment_changes(self, kwargs['env'], prev)
         self.prev_env = kwargs['env']
 
-        # run the command line
+    def runcmd(self, argv, *args, **kwargs):
+        self._prepare_for_runcmd(argv, args, kwargs)
         return cliapp.Application.runcmd(self, argv, *args, **kwargs)
 
+    def runcmd_unchecked(self, argv, *args, **kwargs):
+        self._prepare_for_runcmd(argv, args, kwargs)
+        return cliapp.Application.runcmd_unchecked(self, argv, *args, **kwargs)
+
     def parse_args(self, args, configs_only=False):
         return self.settings.parse_args(args,
                          configs_only=configs_only,