tests/migration: Allow longer timeouts

tests/migration: Allow longer timeouts

In travis, with gcov and gprof we're seeing timeouts; hopefully fix
this by increasing the test timeouts a bit, but for xbzrle ensure it
really does get a couple of cycles through to test the cache.

I think the problem in travis is we have about 2 host CPU threads,
in the test we have at least 3:
   a) The vCPU thread (100% flat out)
   b) The source migration thread
   c) The destination migration thread

if (b) & (c) are slow for any reason - gcov+gperf or a slow host -
then they're sharing one host CPU thread so limit the migration
bandwidth.

Tested on my laptop with:
   taskset -c 0,1 ./tests/qtest/migration-test -p /x86_64/migration

Reported-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20201008160330.130431-1-dgilbert@redhat.com>
[thuth: Move the #define to the right location]
Signed-off-by: Thomas Huth <thuth@redhat.com>