EX-4270 snapshot: avoid call quota op recursively

EX-4270 snapshot: avoid call quota op recursively

In ext4_snapshot_test_and_cow, if there is already in some quota
call, it could cause deadlock if the snapshot calls quota function
to allocate space recursively.

[only the change to snapshot-jbd2-rhel7.7.patch]

Lustre-change: https://review.whamcloud.com/45680
Lustre-commit: 4722f1a0ca9d24bf6fa2678659ccf2cb1be5cdf1

Test-Parameters: trivial
Change-Id: Iac354744fcee8955d8e41020f9cee6d433f38e80
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46009
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>