task/install: skip package removal by default

task/install: skip package removal by default

Every teuthology job cleans up its package install after completion.
This was necessary cleanup when we didn't reimage boxes before the use
of FOG as we wanted a "clean" slate for the next job to acquire the
machine. Now this is just unnecessary work which takes up valuable
machine time. For one job I looked at, this takes about 2 minutes.

We should still test that there are no unexpected issues with removing
the packages but this can be delegated to a small subset of smoke tests.
That will be posted in another PR to ceph.git.

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>