autotest regression test: add a single VM (server only) mode

I've found that it's useful to check just the autotest installation steps
with a single VM with increased resources, mainly memory.

First 1G of memory is too little to do things like compiling the GWT client,
2G is OK, but 4G is preferrable. On most development machines (mine included),
starting two VMs with 2G or 4G is usually not a good idea.

To set this single VM (server only) mode, simply set the "vms" parameter to
a single (server) VM name.

Also, be a lot more generous about the installation timeout, as based on my
experience, things like downloading GWT and the git trees can take a long
time (YMMV).

Signed-off-by: Cleber Rosa <crosa@redhat.com>
autotest regression test: make the unittests arguments configurable

So that we can run the shorter set of unittests if desired.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Merge pull request #1350 from clebergnu/autotest_regression

Autotest regression test