utils.py: fix checkout_repo when no HEAD

Fixed:
$ git clone <url>
warning: remote HEAD refers to nonexistent ref, unable to checkout.
$ git rev-parse HEAD
HEAD
fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

Catch the error and avoid that.

And use "git reset --hard" to replace of "git reset --hard HEAD", HEAD is
default for git reset, so they are the same, but the later one reports error
when remote HEAD doesn't exist:
$ git reset --hard HEAD
fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree.
[snip]

$ git reset --hard
No errors.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>

0 files changed, 0 insertions, 0 deletions