Fix Key Error when editing CD ROM path

lxml only accepts strings as parameters when looking
up xml elements. The port for remote ISO was being
passed in as an int, and a KeyError was thrown.

This patch just casts the ints to strings for the
lookups.

Signed-off-by: Christy Perez <christy@linux.vnet.ibm.com>
Fix verification of remote ISO

Currently the entire ISO is grabbed, which times out.
Use httplib to connect to the server and just get
the head of the http object.

Signed-off-by: Christy Perez <christy@linux.vnet.ibm.com>
Add unit tests for remote-backed CD ROM updates.

Adding tests to ensure that updating an existing CD ROM
can be done when using remote ISOs. This is to test for
regression for the libxml KeyError seen when even saving
the same CD ROM ISO as the update.

Signed-off-by: Christy Perez <christy@linux.vnet.ibm.com>