syz-gce: recover after git pull errors
syz-gce: recover after git pull errors

One of builders got into error loop:

Jan 16 20:55:45 syz-gce-next syz-gce[15380]: 2017/01/16 20:55:45 failed to run git [pull]: exit status 128
Jan 16 20:55:45 syz-gce-next syz-gce[15380]: error: Pull is not possible because you have unmerged files.
Jan 16 20:55:45 syz-gce-next syz-gce[15380]: hint: Fix them up in the work tree, and then use 'git add/rm <file>'
Jan 16 20:55:45 syz-gce-next syz-gce[15380]: hint: as appropriate to mark resolution and make a commit.
Jan 16 20:55:45 syz-gce-next syz-gce[15380]: fatal: Exiting because of an unresolved conflict.

No local changes were made to the repo. It was somehow caused by too many changed files or something.

Make pull more robust: in case of any errors re-clone the repo.

google/syzkaller,xairy/syzkaller,hyz0906/syzkaller,hyz0906/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,hyz0906/syzkaller,dotweiba/syzkaller,xairy/syzkaller,dotweiba/syzkaller,xairy/syzkaller,dotweiba/syzkaller,dotweiba/syzkaller,xairy/syzkaller,zoulasc/syzkaller,zoulasc/syzkaller,google/syzkaller,hyz0906/syzkaller,google/syzkaller,google/syzkaller,zoulasc/syzkaller,google/syzkaller,hyz0906/syzkaller,zoulasc/syzkaller