bitbake: Add sanity check progress screen

bitbake: Add sanity check progress screen

This patch adds a sanity check progress screen to hob. The screen
is displayed when Hob executes the sanity check procedure. The screen
is displayed for at least 5 seconds. If a network error is detected,
a special dialog is displayed which lets the user open the proxy
configuration page directly.
Note that currently bitbake triggers the network tests only when
the value of its TMPDIR variable changes, which happens fairly rare
on my system. This is the subject of another bug (#3026).
Version 2 of the patch splits the changes in two parts (sanity.bbclass
belongs to oe-core).

[YOCTO #3025]

(Bitbake rev: b48f1351271cc066ffe919db112b14834a6d8f8f)

Signed-off-by: Bogdan Marinescu <bogdan.a.marinescu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>