CA-110453: raw iSCSI target provided by domU could not be used

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.
refactor: rename
Simplify test by overriding load method
vdi_type is modified by force_tapdisk
Remove duplicated line
Amend commit according to Robert's comments
Fix bug: AttributeError object has no attribute force_tapdisk

As load() is called from __init__(), force_tapdisk was undefined at that point
use existing whitespace convention
Add prerequisite install script
Updated env setup
Updated prerequisites install
build.sh
virtualenv fix
compile snapwatchd
Added test runner
Make run_tests.sh executable
Document how to set up the environment and how to run the unittests
Remove sm prefix
Add .env directory to gitignore
Refactor - move test_ISCSISR.py to tests/