CA-129333: Improve debugging for snapwatchd. Add documentation for xslib wrapper.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Thanos Makatos <thanos.makatos@citrix.com>

(cherry picked from commit 80f2bf6ecc2cc6dfd58e316b9dbefe1563537fbf)

Imported-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>

GitHub: closes #136 on xapi-project/sm
CP-5736: ISCSISR - force_tapdisk

This is a workaround to make it possible to use a domU provided iSCSI
target as a raw iSCSI SR. By using the force_tapdisk parameter during SR
creation, disks will be accessed through tapdisk aio which copies
blocks, preventing page sharing issues between guests. This is a
workaround for the bug CA-110453.

Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

Imported-by: Mate Lakat <mate.lakat@citrix.com>
(cherry picked from commit 8da7ba62bd92bce057ef5b9ce5919a40a2b5b42e)

GitHub: closes #138 on xapi-project/sm
CP-5736: Unit tests

Unit tests and scripts to setup the environment. See tests/README for
details.

Signed-off-by: Mate Lakat <mate.lakat@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

Imported-by: Mate Lakat <mate.lakat@citrix.com>
(cherry picked from commit de8a7cf26aa571d2f39a13b472e0539215a3cd45)

GitHub: closes #138 on xapi-project/sm