xenapi: Add disk config value to xenstore.

To be able to access the value of disk_config from inside the VM,
added the value to xenstore.

Implements blueprint add-disk-config-to-xenstore
Change-Id: I21170252400ffc73f386dbd19aaa9f7a7613bd56
xenapi:populating hypervisor version in host state

This will be used in the scheduler to compare it to the image
properties.
Pulled out conversion of version string into integer to utils.
Partially implements blueprint xen-support-for-hypervisor-versions

Change-Id: Ib2eb91f6f18af6d39f9381daeff7ba9a24b4785a
Add missing tests for db.api.instance_* methods

Add missing and fixed existing tests.

Mostly replaced assertEqual(2, len(result)) by _assertEqualListOfInstances
and some other minor nits.

blueprint db-api-tests

Change-Id: Ia81dc1d75cbceb3ab882a02a66b3d9ce292816c1
Remove duplicated key_pair* tests from test_db_api.

There is some key_pair* tests in old DbApiTestCase
which are duplicated in new KeyPairTestCase.
This patch simply remove them.

blueprint db-api-tests

Change-Id: Ie25054590286d994bc6748ca85944fa65dcf3d4d
Move dnsdomain_* tests in test_db_api to own test case.

There is dnsdomain_* tests in old mixed DbApiTestCase.
This patch moves them to its own test case DnsdomainTestCase.

Missing test_dnsdomain_unregister added.

blueprint db-api-tests

Change-Id: I9c11ff723d3001499ada54786d09ff397e8fb6e2
Merge "Add missing tests for db.api.instance_* methods"
Merge "Remove duplicated key_pair* tests from test_db_api."
Merge "Move dnsdomain_* tests in test_db_api to own test case."
Merge "xenapi:populating hypervisor version in host state"
Merge "xenapi: Add disk config value to xenstore."
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp