binman: Avoid requiring a home directory on startup

This is needed to download tools, but we may not need to do this. At
present binman fails to start if HOME is not set.

Use the current directory as a default to avoid this.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/bintool.py

@@ -43,7 +43,7 @@ FETCH_NAMES = {
 # Status of tool fetching
 FETCHED, FAIL, PRESENT, STATUS_COUNT = range(4)
 
-DOWNLOAD_DESTDIR = os.path.join(os.getenv('HOME'), 'bin')
+DOWNLOAD_DESTDIR = os.path.expanduser('~/bin')
 
 class Bintool:
     """Tool which operates on binaries to help produce entry contents