bootstrapper: improve heuristic for --zephyr-base

We're seeing warnings when people have ZEPHYR_BASE set to the
"<directory>" they pass to "west init -l <directory>".

Avoid them exactly in the situation that <directory> is a zephyr
repository by using the manifest directory as ZEPHYR_BASE. For
upstream, that is correct anyway.

Merge a couple of lines while here as a cosmetic improvement.

Fixes: #167

Signed-off-by: Marti Bolivar <marti@foundries.io>

src/west/_bootstrap/main.py

@@ -224,8 +224,7 @@ to handle any resetting yourself.
 
 def initialize_west(args):
     '''Initialize a West installation in existing project.'''
-    manifest_dir = args.directory or os.getcwd()
-    manifest_dir = os.path.abspath(manifest_dir)
+    manifest_dir = os.path.abspath(args.directory or os.getcwd())
     directory = os.path.dirname(manifest_dir)
 
     manifest_file = os.path.join(manifest_dir, 'west.yml')
@@ -240,9 +239,14 @@ def initialize_west(args):
     #
     # Note: main west will try to discover zephyr base and fail, as it is
     # not fully initialized at this time.
-    # Thus a dummy zephyr_base is provided.
+    #
+    # The real fix is to eliminate post-init, merge the two mains, and
+    # have west init be a special case that doesn't set up
+    # ZEPHYR_BASE. For now, we assume the original argument (or cwd)
+    # is a Zephyr repository, since that's how people are using it in
+    # practice.
     os.chdir(directory)
-    cmd = ['--zephyr-base', directory, 'post-init', '--local',
+    cmd = ['--zephyr-base', manifest_dir, 'post-init', '--local',
            os.path.abspath(manifest_dir)]
     wrap(cmd)