LU-12787 tests: skip project quota if it is disabled

LU-12787 tests: skip project quota if it is disabled

quota_scan touchs project quota in case of errors or logs.
When project quota is not supported, this leads to error:
    Unexpected quotactl error: Operation not supported
    ...
    Some errors happened when getting quota info. Some devices
    may be not working or deactivated. The data in "[]" is inaccurate.

The fix adds a check before touching project quota.

Cray-bug-id: LUS-7811
Test-Parameters: testlist=sanity-quota
Signed-off-by: Alexander Boyko <c17825@cray.com>
Change-Id: Ia733b666d6937ea9e8e99ef856d2ae1246dc44d1
Reviewed-on: https://review.whamcloud.com/36997
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Alexander Zarochentsev <c17826@cray.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>