Drop TEMPEST_LARGE_OPS_NUMBER by 33% to 100

The large-ops test was originally added to prevent regressions of bug
1199433. The number 150 was chosen somewhat arbitrarily because it never
failed on the cloud that it was tested on. But as we add more clouds and
AZs with different performance characteristics this test is starting to
fail.

Although failing this test at 150 is a sign that something is not
performant and doesn't scale well, this test is just here as a
regression test.  Separate bugs will be opened up for nova and neutron
about this issue.

Partial-Bug: #1257626
Partial-Bug: #1250168
Change-Id: Ie11bf4264eb1b26bc2445a99de7267b07b8058ce