androidbuild: Search homedir of $PORTAGE_USERNAME for credentials.

This makes it possible to use `abutil` from within an ebuild file and
still find .ab_creds.json in the user's home directory.

TEST=Unittests pass.
TEST=Used abutil to successfully fetch an image.
TEST=Used an ab:// URL in an ebuild and confirmed emerge-$BOARD works.

Change-Id: Iaa9310de2eb44328d16bfe60e36d26017ea8575e
Signed-off-by: Filipe Brandenburger <>
Reviewed-by: Don Garrett <>
2 files changed