Merge ~smoser/curtin:feature/subcommand-features into curtin:master

[Scott Moser]

Add subcommand 'features'.

The 'features' subcommand just writes the curtin.FEATURES
to standard output, one per line.

see commit message

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:922e78315b010a3ac88d828a31fb0f557b53dbcf
https://jenkins.ubuntu.com/server/job/curtin-ci/1020/
Executed test runs:
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-arm64/1020
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-ppc64el/1020
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-s390x/1020
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=torkoal/1020

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/curtin-ci/1020/rebuild

review: Approve (continuous-integration)

[Ryan Harper (raharper)]

LGTM

review: Approve

diff --git a/curtin/commands/features.py b/curtin/commands/features.py
 new file mode 100644
index 0000000..0f6085b
--- /dev/null
+++ b/curtin/commands/features.py
@@ -0,0 +1,20 @@
+# This file is part of curtin. See LICENSE file for copyright and license info.
+"""List the supported feature names to stdout."""
+
+import sys
+from .. import FEATURES
+from . import populate_one_subcmd
+
+CMD_ARGUMENTS = ((tuple()))
+
+
+def features_main(args):
+    sys.stdout.write("\n".join(sorted(FEATURES)) + "\n")
+    sys.exit(0)
+
+
+def POPULATE_SUBCMD(parser):
+    populate_one_subcmd(parser, CMD_ARGUMENTS, features_main)
+    parser.description = __doc__
+
+# vi: ts=4 expandtab syntax=python
diff --git a/curtin/commands/main.py b/curtin/commands/main.py
index 779bb03..bccfc51 100644
--- a/curtin/commands/main.py
+++ b/curtin/commands/main.py
@@ -16,9 +16,9 @@ VERSIONSTR = version.version_string()
 SUB_COMMAND_MODULES = [
     'apply_net', 'apt-config', 'block-attach-iscsi', 'block-detach-iscsi',
     'block-info', 'block-meta', 'block-wipe', 'clear-holders', 'curthooks',
-    'collect-logs', 'extract', 'hook', 'install', 'mkfs', 'in-target',
-    'net-meta', 'pack', 'swap', 'system-install', 'system-upgrade', 'unmount',
-    'version',
+    'collect-logs', 'extract', 'features',
+    'hook', 'install', 'mkfs', 'in-target', 'net-meta', 'pack', 'swap',
+    'system-install', 'system-upgrade', 'unmount', 'version',
 ]