Fix tests for pt-slave-find

$ prove -vw --trap --timer t/pt-slave-find
[19:06:41] t/pt-slave-find/pt-slave-find.t .. 
1..10
ok 1 - It compiles
ok 2 - slave2 is slave of slave1
ok 3 - Master with slave and slave of slave
ok 4 - --resolve-address option
not ok 5 - Dies if PID file already exists (issue 391)

#   Failed test 'Dies if PID file already exists (issue 391)'
#   at t/pt-slave-find/pt-slave-find.t line 100.
#                   'Can't locate object method "make_PID_file" via package "Daemon" at /home/sveta/src/percona-toolkit/bin/pt-slave-find line 3908.
# '
#     doesn't match '(?^:PID file /tmp/mk-script.pid already exists)'
ok 6 - pt-slave-find gets the right InnoDB version for the master
ok 7 - ...and for the first slave
ok 8 - ...and for the first slave
ok 9 - Summary report format
ok 10 - Sandbox servers
# Looks like you failed 1 test of 10.
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/10 subtests