xenapi: refactor: move UpdateGlanceImage to common

During the review of https://review.openstack.org/41651 it was
recommended to move UpdateGlanceImage to a common library. A bug was
filed to deal with the refactors. This change fixes the first part.

Fixes bug 1220596

Change-Id: I95ae89525b7e6768c5a70364945d5a10cb906d88
xenapi: refactor: move RawTGZImage to common

During the review of https://review.openstack.org/40909 it was
requested, that the RawTGZImage class should be moved to a common
territory, so that others can re-use it later.

Fixes bug 1220596

Change-Id: I0f186c2f81edbd546c0a24d66e4b9c1626373b12
XenAPI: Add versioning for plugins

Because the plugins live on a host seperate to Nova we need an interface
to test whether they are the expected version.  We can't use pip or other
requirement systems as they are cross-machine.

Closes bug 1226622

Change-Id: I58ab669061f51bd87071e2cf0d93d33021001309