amend API.md

Distros is sub-collection of Configuration. It should follow
Configuration definition.

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>
Fix session locking issue

According to http://docs.cherrypy.org/dev/progguide/sessions.html:
by default, the 'locking' mode of sessions is 'implicit', which means
the session is locked early and unlocked late. It causes that while
a request is being processed, all other requests in that session
will be blocked until the request in processing is done.

The patch changes to use the 'explicit' locking mode,  which means
cherrypy will not lock the session on each request and let application
to guarantee the consistence of session data. Currently, we only use
session for authentication, so it adds code to explictly acquireing
and releasing session lock when it touches session data.

Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
support recrusive probe in iso scanning

Now for directory we can probe all ISOs contained in this directory,
but in deep scan scenario we need recrusive probe.
So add path walk to isoinfo.py

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