Add support for --source on command line.

This provides the ability to install from a different source
by providing it on the command line.  So we can boot into a system,
and then run:
  subiquity --source=/tmp/xenial-server-cloudimg-amd64.squashfs
or
  subiquity --source=http://cloud-images.ubuntu.com/.../some.squashfs

And install that image rather than the hard coded paths.

subiquity/cmd/tui.py

@@ -78,6 +78,9 @@ def parse_options(argv):
     parser.add_argument('--click', metavar="PAT", action=ClickAction,
                         help='Synthesize a click on a button matching PAT')
     parser.add_argument('--answers')
+    parser.add_argument('--source', default=[], action='append',
+                        dest='sources', metavar='URL',
+                        help='install from url instead of default.')
     parser.add_argument(
         '--snaps-from-examples', action='store_true',
         help=("Load snap details from examples/snaps instead of store. "

subiquity/controllers/installpath.py

@@ -54,6 +54,10 @@ class InstallpathController(BaseController):
         log.debug("Installing Ubuntu path chosen.")
         self.signal.emit_signal('next-screen')
 
+    def install_cmdline(self):
+        log.debug("Installing from command line sources.")
+        self.signal.emit_signal('next-screen')
+
     def install_maas_region(self):
         # show region questions, seed model
         title = "MAAS Region Controller Setup"

subiquity/models/installpath.py

@@ -28,23 +28,37 @@ class InstallpathModel(object):
 
     path = 'ubuntu'
     # update() is not run, upon selecting the default choice...
-    source = '/media/filesystem'
     curtin = {}
 
+    def __init__(self, sources=None):
+        self.cmdline_sources = sources
+        if sources:
+            self.path = 'cmdline'
+
     @property
     def paths(self):
-        return [
+        cmdline = []
+        if self.cmdline_sources:
+            cmdline = [(_('Install from cli provided sources'), 'cmdline')]
+        return cmdline + [
             (_('Install Ubuntu'),                 'ubuntu'),
             (_('Install MAAS bare-metal cloud (region)'), 'maas_region'),
             (_('Install MAAS bare-metal cloud (rack)'),   'maas_rack'),
         ]
 
+    @property
+    def sources(self):
+        src_map = {
+            'ubuntu': ['cp:///media/filesystem'],
+            'maas_region': ['cp:///media/region'],
+            'maas_rack': ['cp:///media/rack'],
+            'cmdline': self.cmdline_sources}
+        return {self.path + "%02d" % n: u
+                for n, u in enumerate(src_map[self.path])}
+
     def update(self, results):
-        if self.path == 'ubuntu':
-            self.source = '/media/filesystem'
-            self.curtin = {}
-        elif self.path == 'maas_region':
-            self.source = '/media/region'
+        self.curtin = {}
+        if self.path == 'maas_region':
             self.curtin['debconf_selections'] = {
                 'maas-username': ('maas-region-controller maas/username '
                                   'string %s' % results['username']),
@@ -108,7 +122,6 @@ class InstallpathModel(object):
                 '915-maas': ['umount', '/target/proc'],
             }
         elif self.path == 'maas_rack':
-            self.source = '/media/rack'
             self.curtin['debconf_selections'] = {
                 'maas-url': ('maas-rack-controller '
                              'maas-rack-controller/maas-url '
@@ -132,6 +145,7 @@ class InstallpathModel(object):
             }
         else:
             raise ValueError("invalid Installpath %s" % self.path)
+        self.curtin['sources'] = self.sources
 
     def render(self):
         return self.curtin

subiquity/models/subiquity.py

@@ -49,7 +49,7 @@ class SubiquityModel:
             root = os.path.abspath(".subiquity")
         self.locale = LocaleModel(common['signal'])
         self.keyboard = KeyboardModel(root)
-        self.installpath = InstallpathModel()
+        self.installpath = InstallpathModel(sources=common['opts'].sources)
         self.network = NetworkModel(support_wlan=False)
         self.filesystem = FilesystemModel(common['prober'])
         self.identity = IdentityModel()
@@ -135,9 +135,7 @@ class SubiquityModel:
                     '/var/log/installer/curtin-install.log',
                 },
 
-            'sources': {
-                'rofs': 'cp://%s' % self.installpath.source,
-                },
+            'sources': self.installpath.sources,
 
             'verbosity': 3,