Fix sendmail and squid checks

[jessp01]

tests/p_sendmail/20_sendmail_mta.sh

Allow more than 1 second for relevant entries to appear in
/var/log/maillog
With this change, the test will give up after a minute but will check for
the expected pattern in the log every second

This script runs with /bin/sh but really, it will fail in all below
places with multiple POSIX compat shells and was clearly designed to run
with BASH:

if [ $MTA_ACCEPT == 0 ] # W: In POSIX sh, == in place of = is undefined.
if [[ $mail =~ $regex ]] # W: In POSIX sh, [[ ]] is undefined.
if ([ $MTA_ACCEPT == 0  ] && [ $DELIVERED == 0 ]) # W: In POSIX sh, == in place of = is undefined.
egrep -q "${BASH_REMATCH[1]}\:.*stat\=Sent" /var/log/maillog # W: In POSIX sh, BASH_REMATCH is undefined.
echo -e # W: In POSIX sh, echo flags are undefined.

Wherever possible, I replaced == with = (which will work with BASH
and any POSIX compat shell) but since there are other BASH specific
features that are being used, changed to #!/bin/bash

tests/p_squid/squid_test.sh

SKIP_QA_HARNESS is set in runtests.sh (line 17) but if you run this
single test directly, it will fail with:

tests/p_squid/squid_test.sh: line 9: [: : integer expression expected

Fixed by setting SKIP_QA_HARNESS to 1 if it is unset.