Attempt to fix failing grains tests in 2016.3
Attempt to fix failing grains tests in 2016.3

The tearDown appears to only be removing the grain if it matches a
specific value. This may be leading to the grain value not being blank
at the time the next test is run.

Instead of only deleting the grain if it matches a specific value,
instead delete all items from that grain to ensure that it is empty for
the next test.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt