fix bug: xmlutils get node context by context attribute

doc: http://www.xmlsoft.org/python.html
content : returns the content of the node, it is based on
          xmlNodeGetContent() and hence is recursive.
parent, children, last, next, prev, doc, properties:
        pointing to the associated element in the tree,
        those may return None in case no such link exists.

ref: http://www.xml.com/lpt/a/1211
for the ref, we should use context instead of str

bug: https://github.com/kimchi-project/kimchi/issues/69

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>
Signed-off-by: Bing Bu Cao <mars@linux.vnet.ibm.com>
Use #unicode instead of #encoding in Cheetah templates

In Cheetah 2.4.1, the #encoding declaration must be in the beginning of the
template file or it is ignored.
The #unicode declaration can be done in any part of the file in Cheetah 2.4.1
or newer.
So use #unicode instead of #encoding to avoid restricting the declaration
position.
The #unicode and #encoding only differ in the type of text output - #unicode
returns unicode text and #enconding returns string text.

Signed-off-by: Aline Manera <alinefm@br.ibm.com>
Remove 'path' which should not be specified when creating volume

In volume XML, <path> element provides the location at which the volume can be accessed on the local filesystem, as an absolute path.
This is a readonly attribute, so shouldn't be specified when creating a volume.

Signed-off-by: Bing Bu Cao <mars@linux.vnet.ibm.com>
Asynctask: add logging to async task

Error in async tasks are difficult to track without the stack and log.
Add logging to it.

Signed-off-by: Royce Lv <lvroyce@linux.vnet.ibm.com>