Fix wrong use of LCK_WRITE

Fix wrong use of LCK_WRITE

In all top vg read functions only LCK_VG_READ/WRITE can be used.
All other vg lock definitions are low-level backend machinery.

Moreover, LCK_WRITE cannot be tested through bitmask.
This patch fixes these mistakes.

For _recover_vg() we do not need lock_flags, it can be only
two of above and we always upgrading to LCK_VG_WRITE lock there.
(N.B. that code is racy)

There is no functional change in code (despite wrong masking
it produces correct bits:-)