oeqa/sdkext: Add sdk_update.SDKUpdateTest class.

oeqa/sdkext: Add sdk_update.SDKUpdateTest class.

The SDKUpdateTest class test devtool sdk-update mechanism inside
eSDK.

The SDKUpdateTest class search for new sdk if not found uses
the main one then it publish the eSDK into known folder
inside work and it starts a web server for serve the eSDK.

Finally it executes sdk-update over http, the local test is
commented due to bug [1].

[1] https://bugzilla.yoctoproject.org/show_bug.cgi?id=9043

[YOCTO #9089]

Signed-off-by: Aníbal Limón <limon.anibal@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>