checkbox-touch: fix embedded provider loader after API changes

This patch fixes the embedded provider plug-in to adhere to the extended
plug-in API.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
"automatic merge of lp:~zkrynicki/checkbox/fixes/ by tarmac [r=kissiel][bug=1236377,1236505,1243610,1254189,1254191,1255066,1255085,1265748,1267794,1273100][author=zkrynicki]"