Revert "Revert "CA-114341: check return value of LVHD plugins""

This reverts commit 7d104f5720b444c67e1303b107d4532a8532e925.
Revert "revert CA-114341 patches"

This reverts commit 5d1fe87240d43e2c31bce5dade4f6261d234b0f5.
CA-114341: increase lock retry count

The current value of lock retry is too small and results in VDI.activate
giving up trying to acquire the lock too early. Doubling this value
seems to rectify the problem.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>