Bug 1640837: Proper import of blogposts

If we didn't wrap the blogpost description in a <div></div> it failed
to fully make the content. This is fine for our made leap2a but fails
for ones made via 3rd party systems, like moodle.

The problem was how we extracted the info from the DOM $xml

Test with the leap2a files in the bug report

behatnotneeded

Change-Id: Iedb88a05b332a38305e9304f358d3e424b1973f4
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>