testsuite.at: Workaround for carriage returns on windows.

In unit tests, we compare text written in logs or stdout/stderr
to figure out the success or failure of tests. In Windows,
since new line is represented by CR+LF, autoconf tests run in
MinGW environment fail.

Asking diff to ignore trailing carriage returns is one way
to solve the problem

Suggested-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>