oeqa/rpm.py: Increase timeout and add debug output

[Yocto #14346]
Systemd may be slow in killing pam session sometimes [1][2]. It may cause rpm
test to fail because there's process (sd_pam) running and own by "test1" user
after timeout.
Increasing timeout to 2 mins and assert earlier with debug output if
there's such process(es). If increasing of timeout doesn't help we may
want to force deletion of the user as [2] suggests.

[1] https://github.com/systemd/systemd/issues/8598
[2] https://access.redhat.com/solutions/6969188



Signed-off-by: Pavel Zhukov <pavel@zhukoff.net>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>