ovs-vswitchd.at: Fix "start additional ovs-vswitchd process" test

NetBSD implementation of wc command outputs extra whitespaces
like the following.  Tweak the test to success on such environments.

    % echo hoge|wc -l|hexdump -C
    00000000  20 20 20 20 20 20 20 31  0a                       |       1.|
    00000009
    %

The failing test was introduced by
commit 6bef3c7ca859f208239ca61ec3b25c09a3571553
("bridge: Fix high cpu utilization.")

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Acked-by: Joe Stringer <joestringer@nicira.com>