Add support for snap create-user on Ubuntu Core images.

Ubuntu Core images use the `snap create-user` to add users to an
Ubuntu Core system. Add support for creating snap users by adding
a key to the users dictionary.
  users:
    - name: bob
      snapuser: bob@bobcom.io

Or via the 'snappy' dictionary:
  snappy:
    email: bob@bobcom.io

Users may also create a snap user without contacting the SSO by
providing a 'system-user' assertion by importing them into snapd.

Additionally, Ubuntu Core systems have a read-only /etc/passwd such that
the normal useradd/groupadd commands do not function without an additional
flag, '--extrausers', which redirects the pwd to /var/lib/extrausers.

Move the system_is_snappy() check from cc_snappy module to util for
re-use and then update the Distro class to append '--extrausers' if
the system is Ubuntu Core.

1 files changed, 4 insertions, 14 deletions

diff --git a/cloudinit/config/cc_snappy.py b/cloudinit/config/cc_snappy.py
index 36db9e67..e03ec483 100644
--- a/cloudinit/config/cc_snappy.py
+++ b/cloudinit/config/cc_snappy.py
@@ -257,24 +257,14 @@ def disable_enable_ssh(enabled):
         util.write_file(not_to_be_run, "cloud-init\n")
 
 
-def system_is_snappy():
-    # channel.ini is configparser loadable.
-    # snappy will move to using /etc/system-image/config.d/*.ini
-    # this is certainly not a perfect test, but good enough for now.
-    content = util.load_file("/etc/system-image/channel.ini", quiet=True)
-    if 'ubuntu-core' in content.lower():
-        return True
-    if os.path.isdir("/etc/system-image/config.d/"):
-        return True
-    return False
-
-
 def set_snappy_command():
     global SNAPPY_CMD
     if util.which("snappy-go"):
         SNAPPY_CMD = "snappy-go"
-    else:
+    elif util.which("snappy"):
         SNAPPY_CMD = "snappy"
+    else:
+        SNAPPY_CMD = "snap"
     LOG.debug("snappy command is '%s'", SNAPPY_CMD)
 
 
@@ -289,7 +279,7 @@ def handle(name, cfg, cloud, log, args):
         LOG.debug("%s: System is not snappy. disabling", name)
         return
 
-    if sys_snappy.lower() == "auto" and not(system_is_snappy()):
+    if sys_snappy.lower() == "auto" and not(util.system_is_snappy()):
         LOG.debug("%s: 'auto' mode, and system not snappy", name)
         return