PXE driver should rmtree directories it created

Baremetal PXE driver was failing to delete the per-instance tftpboot and
image directories which it created when the instance was deleted. This
happened partly because of dangling files within the directory, and
partly because 'unlink' does not remove directories and the error was
squelched.

Now, when destroy()ing an instance, PXE driver will call shutil.rmtree()
on the per-instance directories which it created.

Fixes bug 1101048.

Change-Id: I682d0264288add488ea23e5d5200357b7be52dd9
Baremetal/utils should not log certain exceptions

unlink_without_raise was logging exceptions when it failed to unlink a
file, which is confusing since it is often called on non-existing files.

create_link_without_raise was also logging exceptions when it failed
to create a symlink.

This patch corrects this behaviour; both functions now explicitly check
for the type of error they expect, and then suppress that. If another
type of OSError is encountered, a warning is logged. This patch also
adds unit tests for both functions.

fixes bug 1097931.

Change-Id: Ie36f59dce34a6c67765770c5f968c003003acc88
ensure failure to inject user files results in startup error

This was the case in Essex but was inadvertantly changed in:
folsom-2-95-g0d166ca.

* nova/virt/disk/api.py: Refactor to allow specifying
mandatory injection items, that result in an exception
on failure to inject.
* nova/virt/libvirt/driver.py: Specify that user 'files'
are mandatory items and thus result in VM startup failure
unless injected successfully.
* nova/tests/test_virt_disk.py: A new test for the
separate warning and error cases.

Fixes bug: 1095744
Change-Id: Idab5c4294c1cb52098ce44a7aae957a44fb2674f
Fixes task_log_get and task_log_get_all signatures

Fixes signatures for the above methods in nova/db/api.py
based on the recent TaskLog refactor on sqlalchemy/api.py.
Also adds unit tests for TaskLog.

Fixes Bug 1102652.

Change-Id: Id7ce74b8941d9eb6a50dfbfaa62e0fe05dd467c2
Add system_metadata to db.instance_get_active_by_window_joined

Without this compute/utils/notify_usage_exists() throws an
exception when looking for system_metadata in the instance data

Change-Id: I3606aa18b1aa69f98de820840c080f848af56157
Merge "Add system_metadata to db.instance_get_active_by_window_joined"
Merge "Fixes task_log_get and task_log_get_all signatures"
Merge "ensure failure to inject user files results in startup error"
Merge "PXE driver should rmtree directories it created"
Merge "Baremetal/utils should not log certain exceptions"