xenapi: Remove dead code, moves, tests

Related to blueprint xenapi-volume-drivers

Some changes to improve the quality and readability of the existing
code, and to help introducing a clean volume driver concept.

remove:
    dead sm code
move:
    volumeops.introduce_sr -> volume_utils.introduce_sr_unless_present
    volumeops.forget_sr -> volume_utils.forget_sr_if_present
rename:
    volumeops.connect_volume -> _connect_volume
    (to communicate, that it is an internal method)
add tests:
    volumeops.disconnect_volume

Change-Id: Ie5457c3d7823ed77f7ad90252d0c16558e8cfb4f
Fix lintstack check for multi-patch reviews

Some patches in gerrit depend on other patches that are not yet
approved, i.e. not yet landed on master. In this patch lintstack
deals with these cases by currectly generating the right commit
to compare against to further reduce pylint errors.

Part of bp/lintstack

Change-Id: I77622a44949ad2b442d9f2cce6c807e1581830c7
Added sample tests to FlavorSwap API.

Partially implements blueprint nova-api-samples
Fixes bug 1096653

Change-Id: I9a6ca8a023bf0f3404b3a9af635dd29a7a584aa3
Merge "Added sample tests to FlavorSwap API."
Merge "xenapi: Remove dead code, moves, tests"
Merge "Fix lintstack check for multi-patch reviews"