port format inspector tests from glance

This commit is a direct port of the format inspector
unit tests from glance as of commit
0d8e79b713bc31a78f0f4eac14ee594ca8520999

the only changes to the test are as follows

"from glance.common import format_inspector" was updated to
"from nova.image import format_inspector"

"from glance.tests import utils as test_utils"
was replaced with "from nova import test"

"test_utils.BaseTestCase" was replaced with "test.NoDBTestCase"

"glance-unittest-formatinspector-" was replaced with
"nova-unittest-formatinspector-"

This makes the test funtional in nova.

TestFormatInspectors requries qemu-img to be installed on the
host which would be a new depency for executing unit tests.
to avoid that we skip TestFormatInspectors if qemu-img
is not installed.
TestFormatInspectorInfra and TestFormatInspectorsTargeted
do not have a qemu-img dependency so
no changes to the test assertions were required.

Change-Id: Ia34203f246f0bc574e11476287dfb33fda7954fe
(cherry picked from commit 838daa3)
(cherry picked from commit 66205be)
(cherry picked from commit 497abea)
(cherry picked from commit 58cd955)

Author: SeanMooney